GB1586127A - Light polarizing materials particularly for use in light valves - Google Patents

Description

(54) LIGHT POLARIZING MATERIALS PARTICULARLY FOR USE IN LIGHT VALVES (71) We, RESEARCH FRONTIERS IN CORPORATED, of 31 Cain Drive, Plainview, New York, United States of America, a corporation organised under the Laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment This invention relates to light polarizing materials particularly for use in light valves; more particularly, it relates to light-polarizing perhalide materials having improved properties and especially to colloidal particles of such materials.

Light-polarizing materials of many types are well known and have been used commercially for a variety of purposes including use as polarizing filters in instruments, sunglass lenses, and as part of fluid suspensions used as the working fluid in light valves.

Perhalide (sometimes also referred to as "polyhalide") particles constitute one class of light-polarizing materials. Perhalide particles of many types have been studied by many investigators. Extensive studies were carried out in the 19th century by Jorgensen, and products incorporating periodide light-polarizing particles were produced in the 20th century by others, for example in set suspensions used in sheet polarizers.

One problem associated with perhalide particles, especially organic perhalide particles in suspension; has been a need to improve the stability thereof, particularly with respect to heat and exposure to chemicals.

A second problem associated with the perhalide particles is that it has not been possible heretofore consistently to obtain stable particles of a sufficiently small size.

Small size is important in a suspension in order to avoid significant amounts of light scatter and to lessen the tendency of particles to agglomerate when a suspension thereof is used in a light valve.

The ability to produce particles of ex extremely small size is important for another reason, namely that if such particles when initially formed are extremely small, it is possible to control the growth thereof during the chemical process wherein particles and suspensions are produced, so as to produce particles of a somewhat larger optimum or desired size.

Light valves incorporating fluid suspensions have been known for many years.

Fluid suspensions of herapathite particles, an unstable light-polarizing periodid e material, have heretofore been commonly preferred, although other types of particles have been suggested. In general, the shape of the particles used in such a light valve should be such that in one orientation they intercept more light than in another orientation. Particles which are - needle-shaped, rod-shaped, lath-shaped, or in the form of thin flakes, have been suggested. The particles may variously be for example, lightabsorbing or light-reflecting, polarizing, birefringent, metallic or non-metallic. In addition to herapathite, many other materials have been suggested, such as graphite, mica, garnet red, aluminium and periodides of alkaloid sulphate salts. Preferably, dichroic, birefringent or polarizing crystals are employed.

Very finely divided or minute particles, preferably colloidal, are employed and are suspended in a liquid in which the particles are not soluble, and which is of suitable viscosity and relatively high electrical resistivity. In order to help stabilize the suspension when in the non-actuated state, a protective colloid, preferably a suitable polymer, should be used to prevent agglomeration or settling.

Both electric and magnetic fields have been suggested for aligning the particles, although electric fields are more common.

To apply an electric field, conductive area electrodes are provided 6n a pair of oppositely disposed walls of the cell. and an electric potential applied thereto. The elec trodes may be thin transparent conductive coatings on the inner sides of the front and rear walls of the cell, thereby forming an ohmic type cell wherein the electrodes are in contact with the fluid suspension. It has also been suggested to cover the electrodes with a thin layer of transparent material such as glass, in order to protect the electrodes. Such thin layers of glass form dielectric layers between the electrodes and the fluid suspension, and the cells may be termed capacitive cells. Direct, alternating and pulsed voltages have been applied to the electrodes in order to align the particles in the fluid suspension. When the voltage is removed, the particles return to a disoriented random condition due to Brown ivan movement.

Commonly the front and rear walls of the cell are transparent, for example, panels of glass or plastic. With no applied field, and random orientation of the particles, the cell has a low transmission to light and accordingly is in its closed condition. When a field is applied, the particles become aligned and the cell is in its "open" or light-transmitting condition. Instead of making the rear wall transparent, it may be made reflective or a reflective layer may be placed behind it.

In such case light is aborbed when the cell is unenergized and is reflected when the cell is energized. These principal actions may be modified by employing light-reflecting rather than light-absorbing particles.

As aforesaid, one of the most common materials heretofore used in light valve suspensions is herapathite as disclosed in U.S. Patent Nos. 1,951,644 and 1,995,923. Herapathite is quinine bisulphate periodide, the formula for which is stated in the Merck Index (8th Edition) as 4C2"W4N2O2.3H3SO4.2HI.[4.6H20. (The Merck Index is published by Merck & Co.

Inc., Rahway, New Jersey, U.S.A. Herapathite, although an effective polarizing material, is not stable either to heat or to small or even trace amounts of certain chemicals. Because, in many uses, suspensions are subject to exposure to either or both conditions, it is important and usually essential that the particles and suspension not be subject to degradation due to heat or exposure to chemicals during or after the formation thereof.

It is particularly important to avoid deterioration of particles and suspension, so that the suspension may be used as the working material in light valves. For example, it has been observed that a suspension of herapathite particles suspended in isopentyl acetate liquid or other similar liquid esters, together with the Dolymer nitrocellulose which is used to help keen the particles suspended in the manner of the prior art, will change colour from blue initially to red-purple after a period of several months, even at room temperature.

At higher temperatures the colour degradation may be even more severe and takes place much more rapidly.

Also, in order to prepare a suspension of herapathite or the improved materials according to the present invention the particles must be prepared in the presence of solvents, some of which may remain in trace amounts in the final fluid suspension.

If such chemical solvents degrade the suspended particles, as is evidenced, for example by a colour change or a loss in the optical density of the suspension, the particles and suspension are unlikely to be commercially usable over a long period of time. Accordingly, herapathite is an inferior material for use in a light valve suspension because it partially decomposes when in contact with common solvents, such as methanol, an alcohol, and 2-ethoxyethanol, an ether-alcohol, which liquids or others similar to them are often necessarily present during particle formation. Degradation products of the aforesaid nitrocellulose, such as nitrous acid, also seem to attack herapathite.

Accordingly, efforts have been made over the years to find light-polarizing materials that were more stable than herapathite. One such herapathite-like material is described in U.S. Patent No. 2,178,996 whereby a solution of a cinchona alkaloid sulphate is reacted with ammonium iodide and iodine.

A possible formula for one such compound would be the same as the above formula for herapathite, but with ammonium iodide, NHj, substituted for Hl, which is hydriodic acid.

Some additional possible iodides which may be substituted for HI to form similar compounds and which are mentioned in U.S. Patent No. 2,289,712 include: potassium iodide, sodium iodide, magnesium iodide, barium iodide, arsenic triiodine, antimony triiodide, stannic iodide and ferrous iodide.

Unfortunately, none of the alternative iodides to HI mentioned in the preceding two paragraphs permits one to produce, consistently and uniformly, particles which are small enough to permit controlled particle growth during formation so as to reach the desired colloidal size range for use in a light valve suspension. The particles used in a light-valve suspension should be small enough to avoid substantial light scattering and pronounced tendency to agglomerate when the suspension is subjected to an electric field to activate the light valve, but large enough so that it is not necessary to use an undesirably high field or voltage gradient to orient the particles.

The present invention relates to a light polarizing perhalide (alternatively termed "polyhalide") of an alkaloid acid salt having incorporated in its molecular structure at least one halide of calcium, rubidium or cesium, the perhalide being the reaction product of an alkaloid acid salt (or hereinafter defined), elemental iodine and the halide.

(By the term "alkaloid acid salt" is meant a compound of the type obtainable by reaction of an alkaloid with an acid).

The present invention also relates to a process for the preparation of such a perhalide which comprises a process for the preparation of a perhalide as claimed in claim 1 which comprises reacting an alkaloid acid salt, elemental iodine and a halide of calcium, rubidium or cesium.

As mentioned above, the present invention relates to light-polarizing materials and particularly to materials which may comprise the suspended particles in suspension, e.g. colloidal suspensions for use in liquid suspension light valves. The suspended material in such a liquid suspension must be able to withstand the effects of contact with various chemicals, specifically lower alcohols and ether-alcohols, and such materials and suspensions thereof should be able to withstand exposure to temperature substantially above room temperature for a reasonably long period of time.

The present particles are light-polarizing perhalide particles, preferably periodide particles.

The general process for forming the particles is as follows. A suitable organic or inorganic material called the "starting material" is reacted with an appropriate acid to form a salt, called the "precursor".

The precursor is then dissolved in an appropriate liquid medium, and, preferably in the presence of a polymeric protective colloid, is then reacted with effective amounts of a halogen element and a halide to produce perhalide particles.

Various suitable starting materials may be employed. For example, a substance whose sulphate salt, if reacted with iodine and an inorganic iodide, such as HI or KI, will form a light-polarizing perhalide compound, is a suitable material. An example of such an organic material is quinine.

In the previous paragraph, sulphate salts are mentioned. These are salts formed by reacting a starting material with sulphuric acid, an inorganic acid. Sulphuric acid, however, is not the only appropriate acid usable in forming light-polarizing perhalide particles including the present materials. It has been found that polybasic organic acids and hydroxy and polyhydroxy polybasic acids, are also appropriate for such use. Examples of such organic acids include mucic acid, terephthalic acid and pyromellitic acid, although it should be appreciated that a vast number of other acids would also be appropriate, provided that they meet the aforesaid criteria.

Although various iodides have been men tioned in the prior art as possible substitutes for HI in making more stable herapathite-like periodide particles, particles that incorporate these iodides have been found to be inadequate for use in polarizing suspensions, e.g. light valve suspensions, because they either generally produce larger than colloidal size particles, which in suspension scatter a substantial amount of light, or because they produce a heterogeneous mixture of particles of many sizes including some in the colloidal range, but having a largest dimension of nearly 1 micron.

Particles that have a largest dimension of more than or nearly 1 micron are far less useful in a light valve suspension than smaller particles, because the larger particles have a much more pronounced tendency to agglomerate when an electric field (AC voltage) is applied across the suspension in the light valve to cause the anisometrically shaped particles to align.

Therefore, it is both surprising and useful to have discovered that much smaller, and in some cases, extremely small and stable colloidal particles may be formed if certain particular inorganic halides are used in forming perhalide particles instead of those cited in the prior art.

In particular, it has been found that calcium iodide, Cay2, cesium iodide, CsI, and rubidium iodide, RbI, accomplish the desired results.

The following Examples illustrate the present invention.

EXAMPLE 1 describes the preparation of a typical perhalide, wherein Cal2 is used as the inorganic iodide.

EXAMPLE I Process and Formulation for Making Dihydrocinchonidine Sulphate Periodide A typical formulation and process which may be used to prepare dihydrocinchonidine sulphate periodide is as follows: Solution A 3.75 g. dihydrocinchonidine sulphate 20.00 g. 2-ethoxyethanol 10.00 g. HdO Solution B 10.00 g. tricresyl phosphate (TCP) 42.52 g. of a 33 1/3% solution of nitro cellulose in 2-ethoxyethanol.

The nitrocellulose should be a mixture of low viscosity (18.6 cps) and high viscosity (17 second) types, 50% each.

Mix Solution A with Solution B. This combination mixture is called Solution C.

Solution D 0.49 g. CaI2 12.00 g. n-propanol Then add: 3.04 g. I2 35.00 g. TCP Shake well for 15 minutes.

Solution C is combined with Solution D, with vigorous mixing. In less than 1 minute a product will form having a deep blue colour in -a gel formation. This product, which includes a very large number of ex extremely small particles is sometimes referred to as a "wet paste".

Drying may be accomplished by spreading the wet paste as a film, approximately 12 mils thick, on a glass plate, and then allowing the volatile solvents in the paste to come off. For film 12 mils thick, about 3 hours is required for drying. The film in any event should be dried until there is no significant odour from it. The resulting product is sometimes called a "dry paste".

Tricresyl phosphate, a high-boiling point plasticizer, may be used in the above formulation, but its use is optional. However, its use may facilitate the spreading of a wet paste and subsequent dispersion -of. a dry paste.

After drying, a paste may be dispersed into a suspending medium. To accomplish this, the dry paste should first be shaken, ground, or otherwise well mixed into a suspending medium to make a suspension.

Various liquids or combinations of liquids which have a relatively high electrical resistivity, do not degrade or attack the particles or other components of the suspension, and which dissolve the protective colloid, such as a nitrocellulose polymer, which is used in the suspension to stabilize it, may be employed as a suspending-medium. Examples of suspension liquids include esters, such as isopentyl acetate, dioctyl phthalate, diisodecyl adipate and para-nonylphenyl acetate.

Non-solvents for the polymer may also- be used to some degree as part of the suspending medium if they do not cause the polymer to precipitate out.

The suspension may, for example, be well dispersed by subjecting an undispersed mixture of dried - paste and liquid suspending medium to ultrasonic agitation for a sufficiently long time, which may require in excess of 10 hours using a Bransonic 32, an ultrasonic mixer sold by the Branson Instrument Co. of Stamford, Connecticut, U.S.A. Additional liquid suspending media or other materials may be added to the suspension after its dispersion in order to make it less concentrated or for other purposes, such as altering its -viscosity.

The dispersed suspension may be cleaned.

One method for accomplishing this is to add to the suspension a sufficiently large quantity of a liquid that is a non-solvent for the polymeric protective colloid, so as to cause the polymer to precipitate from solution. Because the polymer is bonded to the suspended particles, the latter are also dragged out of suspension when the polymer is precipitated. For example, if the polymer is nitrocellulose, hexane may be used as the non-solvent to cause precipitation. The supernatant may be discarded and the precipitated particles and polymer resuspended in a suitable suspending medium. - In such case it is usually preferable vigorously to disperse the new suspension, e.g. by ultrasonic mixing and agitation.

Particle size fractions may be selected from the suspension by conventional centrifugation methods. The relatively large particles in such a suspension may usually be removed by centrifuging at 4700 r.p.m. for about 20 minutes.

Although calcium iodide is used as the iodide in EXAMPLE 1, the other iodides, CsI or RbI, may be used in its stead.

The quantity of iodide needed when an alternative iodide is used varies somewhat from case to case depending on the molec ular weight of the iodide, but may be easily estimated by conventional chemical methods from the data for CaI2 given in EXAMPLE 1.

The halide in the polarizing material need not be iodide. For example, a bromide may be used. Calcium bromide, CaBr2, has, for example, been found to make excellent polarizing crystals as shown in EXAMPLE 2. Likewise, CsBr or RbBr may be employed.

EXAMPLE 2 EXAMPLE 1 is repeated, except that 0.88 g. of CaBr2 is substituted for 0.49 g.

of Cay,, with similar results.

Substitution of bromine atoms for an iodine atoms tends to change the spectral characteristics of the resulting polarizing particles, generally shifting them from dark blue for a periodide toward the red-brown for a perbromide, with intermediate shades expected for particles incorporating a combination of bromide and iodine, of iodide and bromine. The term "perhalide" as used herein includes all such combinations.

The starting material need not be cinchonidine. EXAMPLES 3, 4, 5 and 6 relate to other starting materials which similarly may be reacted and processes as aforesaid to form light-polarizing particles.

EXAMPLE 3 EXAMPLE 1 is repeated, but with dihydroquinine sulphate substituted for dihydrocinchonidine sulphate, with similar results.

EXAMPLE 4 EXAMPLE 1 is repeated, but with dihydroquinidine sulphate substituted for dihydrocinchonidine sulphate, with similar results.

EXAMPLE 5 EXAMPLE 1 is repeated, but with dihydrocinchonine sulphate substituted for dihydrocinchonidine sulphate, with similar results.

EXAMPLE 6 EXAMPLE 1 is repeated, but with quinine bisulphate substituted for dihydrocinchonidine sulphate, and with water omitted from the formulation, with similar results.

EXAMPLE 7 EXAMPLE 6 is repeated, but with CsI substituted for CaI2, with similar results.

EXAMPLE 8 EXAMPLE 6 is repeated, but with RbI substituted for Caws, with similar results.

Also, as previously mentioned above, appropriate acids may be used instead of sulphuric acid to form the precursor salt employed in EXAMPLES 9 to 11, with similar results.

EXAMPLE 9 EXAMPLE 1 is repeated, except that dihydrocinchonidine mucate is substituted for dihydrocinchonidine sulphate, with similar results.

EXAMPLE 10 EXAMPLE 1 is repeated, except that dihydrocinchonidine terephthalate is substituted for dihydrocinchonidine sulphate, and a small amount of concentrated sulphuric acid (at least 0.25 g.) is added to the reaction mixture to facilitate the reaction, with similar results.

EXAMPLE 11 EXAM PLE 1 is repeated, except that dihydrocinchonidine pyromellitate is substituted for dihydrocinchonidine sulphate, and a small amount of concentrated sulphuric acid (at least 0.25g.) is added to the reaction mixture to facilitate the reaction with similar results.

As is evident from EXAMPLE 1, the particles are formed in a chemical environment that may include alcohols, e.g. npropanol, and ether-alcohols, e.g. 2-ethoxyethanol. The present polarizing materials have been found to be highly stable in such environments relative to other known periodide polarizing particles. The chemical stability of a dry paste with respect to a given solvent may be readily ascertained by mixing a specific quantity of the paste into a quantity of the solvent and observing whether a change in the colour of the paste takes place and, if so, at what rate. This may be compared with the colour of the paste when it is dispersed in a known nonsolvent for the particles, such as dioctyl phthalate (DOP) or dioctyl adipate (DOA), or a combination of DOP or DOA with a halogenated liquid, such as dibromotetrafluoroethane. One may test bare particles for the chemical stability thereof by following the aforesaid test procedure after first having prepared a paste without polymer or plasticizer present. If a solvent attacks or dissolves the bare particles, a strongly tinted solution may be observed, while little or no tint is observed in the case of non-solvent.

The exteremely small colloidal size of many of the present particles may be confirmed by electron micrographs. Also, the size may be predicted by observing the decay time of a suspension thereof in a light valve.

Large particles of the prior art may require up to several hundred milliseconds to disorient after being oriented in a light valve by an electric field, and the field turned off.

By comparison, the present particles have been observed to disorient as rapidly as 1 millisecond.

Particles of this type which when initially formed are extremely small, may be allowed to grow larger controllably by using one or more of a variety of methods. One method of promoting growth is by adding water to the reaction mixture, the more water the more growth. Another method is to decrease the viscosity of the reaction mixture, e.g. by using greater amounts of liquids. On the other hand, growth tendencies may be inhibited by drying a wet paste under conditions of low relative humidity.

Suspensions of the present light-polarizing particles have been used successfully as the working fluids in liquid suspension light valves, as described above. Light valves may use continuous area electrodes within the active region of the cells, or the electrodes may be formed in patterns so as to exhibit a desired display. Furthermore, instead of allowing light to pass through the cell from front to rear, the rear surface may be made reflective so as to provide a mirror of variable reflectivity.

U.K. Patent No. 1586122 (Application No.

21213/77) relates, inter alia, to a light valve which comprises a cell containing a liquid suspension comprising: an electrically resistive liquid suspending medium; suspended therein, a plurality of anisometric, polarizing, halogen -- containing particles; and, substantially dissolved therein, a copolymer comprising at least one monomer having a stericallv unhindered functional group, which is a hydroxyl group of an acidic grout and at least one monomer having a branched group, the distance from the back bone of the copolymer to the most distant sterically unhindered functional group being less than the distance to the terminal carbon atom of the branched group.

U.K. Patent No. 1586123 (Application No.

21214/77) relates, inter alia, to a light valve which comprises a cell containing a liquid suspending medium, suspended therein, particles of one or more halogenated alkaloid acid salts (as therein defined) or metal halides and, dissolved therein, a polymeric stabilizer to prevent agglomeration of the particles, the liquid suspending medium comprising a liquid halogenated hydrocarbon having a ratio of halogen atoms to all other atoms therein of greater than 1:1, the halogen atoms of the particles being iodine and/or bromine and the halogen atoms of the halogenated hydrocarbon being of lower atomic weight than the halogen atoms of the particles and at least 60% of the halogen atoms of the halogenated hydrocarbon being fluorine and/or chlorine.

U.K. Patent No. 1586124 (Application No.

21215/77) relates, inter alia, to a light valve which comprises a cell containing a suspension in a liquid suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid.

U.K. Patent No. 1586125 (Application No.

21216/77) relates, inter alia, to a process for the preparation of a light-polarizing material which comprises; hydrogenating an unsaturated bond of a branch chain of an unsaturated alkaloid, forming an acid salt of the resulting saturated compound; and forming a polyhalide of the resulting alkaloid acid salt (as herein defined). We make no claim herein to this process or the product thereof.

U.K. Patent No. 1586126 (Application No.

21217/77) relates, inter alia, to a light valve which comprises a cell containing a suspension in a liquid (as therein defined) suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid, the liquid suspending medium comprising, dissolved therein, a polymeric material for preventing agglomeration of the particles.

SUBJECT TO THE FOREGOING DISCLAIMER, WHAT WE CLAIM IS: 1. A light polarizing perhalide of an alkaloid acid salt having incorporated in its molecular structure at least one halide of calcium, rubidium or cesium, the perhalide being the reaction product of an alkaloid acid salt, (as hereinbefore defined), elemental iodine and the halide.

2. A perhalide as claimed in claim 1 wherein the alkaloid is a quinine alkaloid.

3. A perhalide as claimed in claim 2 wherein the quinine alkaloid is selected from quinine, dihydroquinine, dihydrocinchonidine, dihydrocinchonine and dihydroquinidine.

4. A perhalide as claimed in claim 2 wherein the alkaloid acid salt is hydrocinchonidine sulphate.

5. A perhalide as claimed in any of claims 1 to 4 wherein the halide is a bromide or iodide.

6. A perhalide as claimed in claim 1 substantially as herein described.

7. A perhalide as claimed in claim 1 substantially as herein described with reference to the Examples.

8. A process for the preparation of a perhalide as claimed in claim 1 which comprises reacting an alkaloid acid salt, elemental iodine and a halide of calcium, rubidium or cesium.

9. A process as claimed in claim 8 substantially as herein described.

10. A process as claimed in claim 8 substantially as herein described with reference to the Examples.

11. A perhalide as claimed in claim 1 when prepared by a process as claimed in any of claims 8 to 10.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   bone of the copolymer to the most distant sterically unhindered functional group being less than the distance to the terminal carbon atom of the branched group.

   U.K. Patent No. 1586123 (Application No.

   21214/77) relates, inter alia, to a light valve which comprises a cell containing a liquid suspending medium, suspended therein, particles of one or more halogenated alkaloid acid salts (as therein defined) or metal halides and, dissolved therein, a polymeric stabilizer to prevent agglomeration of the particles, the liquid suspending medium comprising a liquid halogenated hydrocarbon having a ratio of halogen atoms to all other atoms therein of greater than 1:1, the halogen atoms of the particles being iodine and/or bromine and the halogen atoms of the halogenated hydrocarbon being of lower atomic weight than the halogen atoms of the particles and at least 60% of the halogen atoms of the halogenated hydrocarbon being fluorine and/or chlorine.

   U.K. Patent No. 1586124 (Application No.

   21215/77) relates, inter alia, to a light valve which comprises a cell containing a suspension in a liquid suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid.

   U.K. Patent No. 1586125 (Application No.

   21216/77) relates, inter alia, to a process for the preparation of a light-polarizing material which comprises; hydrogenating an unsaturated bond of a branch chain of an unsaturated alkaloid, forming an acid salt of the resulting saturated compound; and forming a polyhalide of the resulting alkaloid acid salt (as herein defined). We make no claim herein to this process or the product thereof.

   U.K. Patent No. 1586126 (Application No.

   21217/77) relates, inter alia, to a light valve which comprises a cell containing a suspension in a liquid (as therein defined) suspending medium of particles responsive to an electrical field to change the transmission of radiation through the suspension, the liquid suspending medium comprising an ester of a phenol and a carboxylic acid, the liquid suspending medium comprising, dissolved therein, a polymeric material for preventing agglomeration of the particles.

   SUBJECT TO THE FOREGOING DISCLAIMER, WHAT WE CLAIM IS: 1. A light polarizing perhalide of an alkaloid acid salt having incorporated in its molecular structure at least one halide of calcium, rubidium or cesium, the perhalide being the reaction product of an alkaloid acid salt, (as hereinbefore defined), elemental iodine and the halide.
2. 2. A perhalide as claimed in claim 1 wherein the alkaloid is a quinine alkaloid.
3. 3. A perhalide as claimed in claim 2 wherein the quinine alkaloid is selected from quinine, dihydroquinine, dihydrocinchonidine, dihydrocinchonine and dihydroquinidine.
4. 4. A perhalide as claimed in claim 2 wherein the alkaloid acid salt is hydrocinchonidine sulphate.
5. 5. A perhalide as claimed in any of claims 1 to 4 wherein the halide is a bromide or iodide.
6. 6. A perhalide as claimed in claim 1 substantially as herein described.
7. 7. A perhalide as claimed in claim 1 substantially as herein described with reference to the Examples.
8. 8. A process for the preparation of a perhalide as claimed in claim 1 which comprises reacting an alkaloid acid salt, elemental iodine and a halide of calcium, rubidium or cesium.
9. 9. A process as claimed in claim 8 substantially as herein described.
10. 10. A process as claimed in claim 8 substantially as herein described with reference to the Examples.
11. 11. A perhalide as claimed in claim 1 when prepared by a process as claimed in any of claims 8 to 10.