US2988912A - Melting point determining apparatus - Google Patents

Description

June 20, 1961 s. KASMAN 2,988,912

MELTING POINT DETERMINING APPARATUS Filed Nov. 15. 1957 F 4 INVENTOR.

SIDNEY KASMAN STAN LEY H. MERVIS ATTOR N EY United States, Patent 2,988,912 MELTING POINT DETERMINING APPARATUS Sidney Kasman, 14 Ernest Road, Boston, Mass. Filed Nov. 15, 1957, Ser. No.'696,732

7 Claims. (Cl. 73-17) This invention is concerned with apparatus for deter mining physical properties of chemical substances, and, in particular, with apparatus for determining the melting point or freezing point of chemical substances.

A principal object of this invention is to provide apparatus for determining physical properties, such as the melting point or freezing point, of a chemical substance contained in a capillary tube, wherein a rapid rate of heating or cooling is obtained.

A further object of this invention is to provide apparatus of the type described having a low ratio of total heat capacity to the amount of heat input or withdrawal.

Another object ofthis invention is to provide apparatus of the type described which is capable of being used to determine melting points of high melting substances.

These and further objects will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the products possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed disclosure taken in connection with the accompanying drawing wherein:

FIGURE 1 is a front view of one apparatus constructed in accordance with this invention, including means for receiving and heating samples;

FIG. 2 is a top view of the embodiment depicted in FIG. 1;

FIG. 3 is a top view of viewing and illuminating means for use in this invention;

FIG. 4 is a front view of the viewing and illuminating means embodied in FIG. 3; and

'FIG. 5 is a side view of one embodiment of a cooling means suitable for use in the apparatus of FIGS. 1 and 2.

Apparatus used to determine melting points of chemical substances contained in capillary tubes commonly employ high boiling fluids. Such equipment, however, suffer from safety hazards, such as highly corrosive fluids, ther-- mal instability of some of the high boiling fluids used, and also have a. relatively low upper temperature limit. One

method which has been proposed for obtaining higher.

temperatures is by the use of electrically heated apparatus. United States Patent No. 2,658,382 is an example of such electrically heated melting point apparatus. It has been found, however, that apparatus of that type suifers from low maximum rates of heating and cooling, and thus take unnecessarily long periods to reach the desired temperature and to cool down to permit a subsequent determination of the melting point of another sample. In addition, this apparatus requires the use of multiple heating elements, and the samples are surrounded by a substantially evenly distributed heat conducting mass.

I have discovered that a very effective apparatus of the electrically heated type, having high maximum rates of heating and cooling, may be obtained by the use of a low heat capacity, high thermal conductivitymetal, wherein the ratio of total heat'capacity to heat input is low, and preferably 'is at a minimum, in accordance with the unique structure herein described.

I have found that aluminum is highly suited to the manufacture of such melting point or melting point block apparatus, due to its low specific heat, high thermal con ductivity, cheapness and machineability. Other metals, including alloys, having the requisite characteristics may also be used, although aluminum (including aluminum alloys) is the preferred material. The apparatus of this invention, constructed of aluminum, has been successfully used in determining melting points up to about 500 C. For substances melting above 500 C., a more refractory material, such as a stainless steel alloy, may be used in constructing this apparatus.

In general, the melting point apparatus of this invention comprises a melting point block, including means for receiving and holding samples of substances whosemelting points are to be determined, means for electrically heating said chamber, means, e.g., a thermometer, for determining the temperature of said samples, and means for illuminating and observing said samples.

Referring to the accompanying drawing, FIG. 1 shows a front view, and FIG. 2 shows a top View of one embodiment of this invention. A melting point block housing 1. contains a-well 3 for a thermometer 5 and a plurality of chambers or wells 7 for receiving sample-holding capil lary tubes (not shown). Suitable electrical heating means 9, for example a cartridge or rod electrical heater, is inserted in a heater well 21 in the housing 1 to provide the necessary heat. Suitable means are provided for retaining the cartridge heater 9 in the heater well 21, e.g., a plate 13 may be mounted, permanently or detachably, so as to extend a s-ufircient distance over the bottom of the heater well 21 to prevent the cartridge heater 9 from falling out. A suitable permanent or removable cover 16, e.g., a plug button, may be employed to seal or cover the top of the,

heater well 211. Thus it will be possible to readily remove or replace the heater cartridge 9. A sleeve or tube 11' extends upward from the housing 1 and surrounds the lower portion of the thermometer 5, inserted into well 25',

to insure proper heating thereof, e.g., it surrounds the thermometer to the height of its immersion line.

The lower portion of the housing 1 preferably containsto the capillary chambers 7. The capillary chambers 7 preferably are each approximately 7 square in cross section. By actual measurement, it has been found thata large sample of commercial melting point capillary tubes fit such square chambers.

A branched or V-tube assembly 29 comprising two arms or segments 15 and '17 and shown in top view in' FIG. 3 and in front view in FIG. 4, provides means of illuminating and viewing the samples. In use, a source of light, e.g., a small electric bulb, is so placed near'one arm of the V-tube assembly, e.g., arm 15, that it illuminates the samples, and the samples are observed by viewing through the other arm of the housing 1 that the viewing area 31 coincides with the sample-containing area of the capillary wells 7 and permits simultaneous viewing of all of said samples. Each.

tube sees the same area, and the crosssection dimensions thereof are determined by the. area occupied by the. sample-containing portion of the capillary .wells. A capil-. lary tube is customarily filled with the sample-to a depth of about two to six mm. Since it is preferable to be able to see the upper surface of the sample, the vertical dimension of the viewing area is about to V2 inch. The horizontal dimension is determined by the width of the the V-tube, e.g., arm 17. The V-tube is mounted on amounting plate 27 haw ing a suitable opening, and the plate 27 is so attached to.

capillary wells and the walls between said wells, and will be about of an inch.

The V-tube assembly may be mounted with the plane containing the tubes horizontal, as shown in FIG. 4, or with said plane in a vertical position. The arms 15. and 17' may be constructed from tubing of either round or rectangular cross section. In a preferred embodiment, the tubing is of rectangular cross section, since this permits the tube to cover the exact area to be viewed, and is fitted with glass covers. A particularly useful V-tube assembly is one wherein the tube plane is vertical, the illuminating tube is mounted at 90 angle to the capillary wells, and the viewing tube is at an angle inclined upwardly therefrom, e.g., about 4070, thus permitting a more comfortable viewing position for the observer.

The V-tube lighting and viewing assembly 29 may be constructed by cutting aluminum tubing and joining the resulting sections, e.g., by soldering, at a suitable angle, e.g., about 40 to 70. The point of the V-tube is cut off to provide a common opening for both tubes, which opening is of such a size that each tube views substantially the same area. The V-tube is attached to an aluminum mounting plate 27 in which an opening 31, coinciding with the V-tube common opening, has been cut. The arms and 17 of the V-tube are cut to the desired length, and the open ends thereof are covered by a suitable transparent cover, e.g., glass, not shown, to prevent air currents, and held in place, for example, by a sprung split ring. The cover of the viewing arm is preferably a magnifying lens so that the small samples may be viewed more easily. The V-tube assembly may be attached by appropriate mounting means, e.g., by the use of screws.

The capillary wells 7 are recessed into an outer surface of the housing 1. They are so constructed as to have three walls provided by the housing 1, and the V-tube assembly is so mounted as to complete the well.

I have found that the V-tube viewing and illuminating assembly is essential to obtaining sharp melting points. It will be noted that the sample undergoing testing is near thesurface of the housing 1 and is not surrounded by heating cartridges. If the capillary wells 7 are simply covered with a glass plate, extended melting point ranges are obtained from samples known to have sharp melting points. This is believed to be the result of the ability of the sample to radiate heat energy through a large solid angle. The V-tube assembly 29 effectively reduces the solid angle through which heat may be radiated by the sample, and sharp melting points are obtained when the V-tube assembly is used.

The completed apparatus may be attached to a ring stand or other support by suitable means, e.g., by leg 23 which is coaxial with the thermometer well 3.

The melting point apparatus of this invention may be constructed from a solid block of aluminum by suitable machining and boring of the block. In a preferred embodiment, all of the block except the V-tube assembly may be cast, and the thermometer and heater wells reamed out or enlarged to the exact dimensions desired. The V-tube assembly may also be made by casting, and the mounting plate may be cast as an integral part thereof.

It will be understood that the dimensions of the melting block may be varied so long as the ratio of total heat capacity to heat input is maintained at or close to the minimum. Thus, corners of the block may be removed to reduce heating mass. The use of the branched or V- tube assembly is particularly important as permitting a significant reduction in the weight and bulk of the housing 1, as contrasted with the use of holes drilled for comparable purposes in housings wherein the samples are positioned inside the housing.

By substituting a source of cooling or heat withdrawal for the electrical heater, the apparatus may be used to obtain freezing, i.e., melting points of normally liquid substances. As illustrated in FIG. 5, a cooling means may comprise a chamber 33 having an inlet 35 emptying near the upper end of the chamber 33, and an outlet 37 positioned at the bottom of said chamber. The chamber 33 is preferably designed to be inserted into the well 21 in lieu of the heating cartridge 9. By circulating suitable coolants, e.g., expanding carbon dioxide, chilled nitrogen or a cold liquid, one may lower the temperature of the housing 1 and thus determine the freezing point of the liquid sample.

It will be noted that the housing 1 preferably is not insulated; this permits rapid natural cooling for subsequent melting point determination, and' it is usually unnecessary to resort to the use of heat exchange techniques. Where the cooling means is employed, it may be desirable to sufiiciently insulate the housing 1 to reduce or prevent moisture condensation thereon. The glass covers of the viewing and illuminating arms 15 and 17 are preferably easily removable in the event of internal condensation in the tubes when the cooling means is employed.

Since certain changes may be made in the above products without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An article of manufacture for determining melting points of chemical substances and having low heat capacity thereby permitting rapid heating and rapid cooling, comprising a mass of a solid of high heat conductivity, said mass having an opening recess in an outer surface thereof for receiving one or more capillary tubes containing samples of said chemical substances; branched tube means including a viewing tube and a light-transmitting tube so joined as to have a common opening providing substantially the same viewable area for each of said viewing and light-transmitting tubes, said common opening being so positioned as to cover at least the samplecontaining portion of said recess; a first well in said mass for receiving a thermometer; a second well in said mass for receiving means for changing the temperature of said mass; said branched tube means transmitting light to, and permitting viewing of, the samples contained in said capillary tubes and reducing the solid angle through which heat may be radiated from said samples.

2. An article of manufacture as defined in claim 1,

wherein each of said viewing and light-transmitting tubes is closed by a transparent cover.

3. An article of manufacture as defined in claim 1, wherein said transparent cover for said viewing tube is a magnifying lens.

4. An article of manufacture as defined in claim 1, wherein said mass comprises aluminum.

5. An article of manufacture as defined in claim 4, wherein said tubes are composed of aluminum.

6. An article of manufacture as defined in claim 1, including means comprising a source of light so positioned as to illuminate said samples through said light-transmitting tube.

7. An article of manufacture as defined in claim 1, including electrical cartridge heating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,982,620 Alleman et al. Dec. 4, 1934 2,036,432 Musante et al. Apr. 7, 1936 2,455,966 Ackley Dec. 14,, 1948 2,658,382 Vanderkamp Nov. 10, 1953

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