US2387561A - Method of treating the rock, aplite - Google Patents

Description

' Oct. 23, 1945. R. F. BRENNER 2,387,561

METHOD OF TREATING THE ROCK, APLITE I Filed March 26, 1945 7 Sheets-Sheet 1 NGFELDSPAR l K FELDSPAR 2 Fig. l

NOIlVSNO'B SBHDNI INVENTOR. Ralph E Brznner:

ATTORNE Y5 Oct. 23; 1945.

R. F. BRENNER METHOD OF TREATING ROCK, APLITE Filed March 26, 1945 7 Sheets-Sheet 2 mo E3555 SE oom INVENTOR. I Ralph EBrznnzc BY j M, W l M ATTORNEYS Oct. '23, 1945. R. F. BRENNER 2,387, I VIETHOD OF TREATI NG THE ROCK, APLITE Filed March 26, 1943 v Sheets-Sheet 3 TEMPERATURE 'F Fig. 3

IVNVENTOK Ralph E Brenner.

BY M, 7 PM ATTORNEYS Oct. 23, 1945. R. F. BRENNER METHOD OF TREATING THE ROCK, APLITE Filed March 26, 1943 '7 Sheets-Sheet 4 'INVENTOR. Ralph E Brenner BY I M, f

r ATTORNEYS Ogit. 23, 1945. R. F. BRENNER METHOD OF TREATING THE ROCK, APLITE Filed March 26, 1945 7 Sheets-Sheet 5 INVENTORI Ralph EBrennert BY I W W M ATTQRNEYS R. F.. BRENNER METHOD OF TREATING THE ROQK, APLITE Oct. 23, 1-945. 2,387,561

'7 Sheets-Sheet 6 Filed March 26, 1945 TEMPERATURE "F Fig. 6

INVENT OR. Ralph E Brznner:

ATTORNEKS V Oct. 23, 1945. R. F. BRENNER I METHOD OF TREATING THE ROCK, AI LITE Filed March 26, 1943 7 Sheets-Sheet 7 Fig. 9

Fig. 7

Fig.1!)

Fig. 14

INVENTOR. Ralph E Brenner BY Y W M +2 Fig. 16

- mp/vs);

Patented Oct. 23, 1945 METHOD OF TREATING THE ROCK, APLITE Ralph F. Brenner, Lancaster, Ohio, assignor to Dominion Minerals, Incorporated, Washington, D. (3., a corporation of Virginia Application March 26, 1943, Serial No. 480,641 2 Claims. (Cl. 241-32) ginia, has the following approximate chemical composition I A l I Per cent Albite (Al 90, An 10) 55' Zoisite 22 Sericite s 13 Microcline Quartz 3 Titanite, garnet, apatiteand clino-zoisite 2 At the present time, considerable difficulty is encountered in grinding the rock aplite due to its excessive hardness, the lack'of cleavage, and the tendency to produce an excessive amount of fines during grinding. In grinding aplite at the present time, a large amount of fines, finer than 200 mesh, are produced because of the nature of the grinding action required to reduce the extremely hard lumps into grains of suitable size. Due to the nature of these fines, a larg percentage of this material is waste material. Also, because of the extreme hardness and lack of cleavage of the 1 aplite, it is necessary to have very rugged and wear-resistant grinding equipment, which is expensive, and still excessive wear occurs.

As indicated in Patent No. 2,304,440, issued to Ralph F. Brenner and Roger D. Dubble, on December 8, 1942, the rock aplite has iron in combined form therein, and it is very desirable to reduce this iron content in order to make the aplite suitable. for useinceramic mixtures, such as in glass batches, orfor. similar uses.

One of the objects of my invention is to treat the rock aplite before grinding in such amanner that its resistance to grinding will be reduced, due to a change in physical structure.

Another object of my invention isto treat the rock aplite before grinding in such a manner that grinding will not only be facilitated but also subsequent treatment to remove the iron content will be facilitated.

Another object of my invention is to treat the rock aplite before grinding in such a manner that excessive wear on the grinding equipment will be reduced to a minimum.

Another object of my invention is'to treat the rock aplite in such a manner before grinding that its resistance to grinding will be greatly reduced and its physical structure changed so that the grinding operation required to reduce the lumps of aplite to suitable grain size will not be of such a nature as to produce a'high percentage of fines.

Another object of my invention is to provide a complet and efiicient process for treating the rock aplite, as mined, to reduce it to the proper grain size and to reduce the iron content thereof.

The rock aplite, as mined, usually consists of lumps of various sizes. As previously indicated, it has been very diflicult to grind these lumps in order to produce'grains of the proper size. I have found that if the'aplite is subjected to a proper calcining or heat-treating operation befor grinding, grinding is facilitated. I have discovered that for this purpose it is desirable to calcine or heat-treat the aplite at a temperature in excess of 1000 F. and up to the fusion point of the aplite, which usually is about 223'? F. The most effective and preferred range of calcining temperatures is between 1650 and 2000" F. The time of heating will depend upon the size of the lumps of the aplite. It is merely necessary to heat the aplite for a period sufiicient for the heat to penetrate completely into the interior of the lumps. After the aplite is subjected to this heat-treatment, it is cooled in air or waterquenched or sprayed. I prefer to either waterquench or spray the aplite.

Although I do not wish to be limited to any particular theory, th calcining or heat-treating operation apparently changes the physical structure of the aplite, causing permanent expansion or dilatation thereof and fracturing preferentially along the grain boundaries thereof. This apparently is the reason for the improvement in the grindability of the aplite and for the production of a greater percentage of ground material of the desired screen size.

In order to establish the grinding characteristics of aplite and to establish the temperature at which calcination should be carried out prior to grinding, certain tests were made. Similar tests were made on other materials, such as soda feldspar, potash feldspar, and quartz, to show that the results obtained by calcining aplite within the ,proper temperature range are caused by properties characteristic of aplite. and not .of the individual minerals contained in the aplite.

The accompanying drawings will aid in understanding these tests and the results obtained. In these drawings:

Figure l is a diagram showing expansion and cooling curves for aplite, soda feldspar, potash feldspar and quartz, heated at temperatures within the range, room temperature to 2000 F.

Figure 2 is a diagram showing curves for grindability indices plotted against calcination temperature obtained from various calcined samples of aplite, soda feldspar, potash feldspar and quartz.

Figure 3 is a diagram showing curves which indicate the percentage increase in grindability, owing to calcination, of calcined samples of aplite, soda feldspar, potash feldspar, and quartz.

Figure 4 is a diagram showing curves in which the percentage of plus 16-mesh material is plotted against temperature for the calcined and uncalcined samples of aplite, soda feldspar, potash feldspar and quartz.

Figure 5 is a diagram showing curves in which the percentage of minus '16 plus IOU-mesh material is plotted against temperature for the calcined and 'uncalcined samples of aplite, soda' feldspar, potash feldspar and quartz.

Figure 6 is a view wherein the curves indicate the percentage increase in minus 16 plus 100- inesh material plotted against temperature for the calcined and uncalcined samples of aplite, soda feldspar, potash feldspar and quartz.

Figure 7 is a reproduction of a photomicrograph of an uncalcined sample of aplite taken under a polarizing microscope at magnifications without crossed nicols.

' Figure 8 is a photomicrograph at 10 magnifications which is the same field as Figure '7 and which was photographed with crossed nicols.

Figure 9 is a crossed nicols photomicrograph at 10 magnifications of a sample of aplite calcined at 1000 Fahrenheit.

Figure 10 is a similar view of a simple of aplite calcined at 1300 Fahrenheit.

Figure 11 is a similar view of a sample of aplite calcined at 1500 Fahrenheit. I

Figure 12 is a similar view of a sample of aplite calcined at 1650 Fahrenheit.

Figure 13 is a similar view of a sample of aplite calcined at 1800 Fahrenheit.

Figur 14 is a similar view of a sample of aplite calcined at 2000 Fahrenheit.

Figure .15 is a similar view of a sample of aplite calcined at 2150 Fahrenheit.

Figure 16 is a photomicrograph at 1 0 magnifications which is the same field as Figure 15 but which was photographed without crossed nicols. To establish the grinding characteristics of the materials in question before calcination and after they had been calcined at various significant. temperatures, it was decided to use the Grindability index method developed by Bond and Maxson* as a means of showing changes in grinding characteristics owing to calcination.

*In addition to tests on aplite, in this work, the effect of calcination on grindability was studied for soda feldspar (albite), potash feldspar (microcline), and quartz. The reason for including soda feldspar, potash, feldspar and quartz in this investigation is that they are major constituents of aplite rock and it was desired to show that in the particular temperature range where calcination renders aplite least resistant to grinding, the effect :is .due to .some change which is inherent in the makeup of aplite and that cannot be accounted for by the physical changes that take place in soda feldspar, potash feldspar and quartz.

The samples of aplite, soda feldspar, potash. feldspar and quartz used in this investigation were. received in lumps, some as coarse as 10 inches. The largest lumps were sledged down to crusher size and then each material was carefully stage crushed to minus inch.

Table 1 which follows gives the chemical composition of the aplite, soda feldspar, potash feldspar and quartz samples.

Table 1.Chemical composition of aplite, soda feldspar, potash feldspar, and quartz samples 1 Blank spaces indicate that no determination was made. Ignition gain.

The mineralogical composition of this same aplite rock has been given previously. The soda Bristol, model A-116, dilatometer machine.

data obtained in these tests.

feldspar was optically identified as albite (A190,

An 10), the potash feldspar as microcline and the quartz as alpha quartz.

In order to determine whether the materials under consideration passed through inversion or transition points on heating and to establish the temperatures at which calcination should be carried out prior to grinding, dilatometer tests were made. The tests were made in a Rockwell- The Rockwell-Bristol dilatometer is an instrument that measures dilatation or elongation with increase in temperature and plots temperaturedilatation and time-dilatation curves.

Figure .1 presents the temperature dilatation This figure was prepared by plotting on rectangular coordinates, inches of elongation as ordinate and temperature in degrees Fahrenheit as abscissa. These four specimens were all dilatometrically treated in the same .manner and presenting them in one figure shows the relative expansion of aplite, soda feldspar, potash feldspar and quartz in the range A. I. M. E. Milling Methods, 1934, pages to 145, and A. I. M. E. Milling Methods, 1939, pages 296 to'300.

roomitemperature to 2000" Fahrenheit and. the contraction as the specimens were allowed to cool to room temperature.

The curve for soda feldspar shows that its elongation is quite uniform :until a temperature of 1650 Fahrenheit is reached, where a transition point occurs and the elongation increases rapidly to six times its previous rate. When it reaches 1800 Fahrenheit, the elongation is slowed down and at 1900 Fahrenheit shrinkage begins. The cooling curve is uniform and shows that soda feldspar does not pass through a transition point on cooling. The vertical displacement between the beginning of the heating curve and the end of the cooling curve shows that the permanent dimensional change is slight.

The curves for potash feldspar show that it has uniform elongation with heating and that it contracts to practically its original length upon cooling. The uniformity of these curves indicate that potash feldspar does not pass through a transition point in the temperature range studied.

The curve for quartz shows that it has a much more rapid elongation than either potash feldspar or soda feldspar and that this elongation is uniform until a temperature of about 1100 Fahrenheit is reached, where the curve flattens off with practically no further elongation up to 1800'? Fahrenheit followed by slight shrinkage up to 2000 Fahrenheit. The chang in the slope of the quartz curve at 1100 Fahrenheitindicates an inversion point and a change from alpha to beta quartz. It is significant that the cooling curve passes through this same inversion point, 1

showing that the change is reversible and a permanent dimensional change does not persist.

The fact that the specimens of soda feldspar, potash feldspar, and quartz return very nearly to their original lengths warrants the conclusion that their permanent expansion caused by heating is slight. a

The aplite expansion curve shows that the elongation-is uniform until a temperature of 1650 Fahrenheit is reached where a slight increase in tween room temperature and 1650 Fahrenheit and maintains this rate to 2000" Fahrenheit. The

expansion curve described for aplite is similar to that described earlier for soda feldspar but the total expansion of the aplite is three times greater.

The cooling curve for aplite does not parallel the heating curve for there is no reverse transi tion at 1650' Fahrenheit and the total contraction is only one third of the expansion. In

marked contrast to the curves for soda feldspar, potash feldspar, and quartz the aplite retains a large permanent deformation.

Two other dilatometer tests were made on aplite the curves for which are not shown in Figure 3. In one of these tests the maximum temperature employed was 1400 Fahrenheit, that is below the aplite transition temperature. The cooling curve came back to the starting point At 1850 Fahrenheit the curve Ti assumes a rate approximately equal to that beof the 27 test samples calcined as above.

showing that when aplite is heated below its transition point, the operation is reversible. In the other test, the aplite was heated to 2000 Fahrenheit, then cooled slowly and heated a second time to2000 Fahrenheit and cooled. The curves for this test showed that the curves for the second heating and cooling followed the first cooling curve, starting and ending at the same point. This is added proof that aplite undergoes a permanent dimensional change when heated to 1650 Fahrenheit,. but that when expanded aplite is again heated, only reversible changes occur.

Calcinwtion tests In view of the facts presented in Figure 1, samples of each of the materials were calcined at the following temperatures: 1000 Fahrenheit, which is below the transition point of any of the minerals; 1300 Fahrenheit, which is above the inversion point for quartz; 1500 Fahrenheit, which is below the transition point in aplite and soda feldspar; 1650 Fahrenheit, which is at the transition point for aplite and soda feldspar; 1800 Fahrenheit, which is near the middle of the aplite transition zone; and 2000" Fahrenheit, which is at the end of the aplite transition zone and the reversing point for quartz. Another temperature was desired in order that the maximum limit or temperature range in which calcining is effective would be established. This was obtained by observing the lowest calcining temperature at which softening of the aplite took place. Although the fusion point of aplite is said to be 2237 Fahrenheit, it becomes soft at 2150" Fahrenheit, so the latter temperature was chosen as the upper limit for the calcining tests.

In the furnace used in calcining these samples, the samples were brought to the desired temperature and. held there for fifteen minutes in a neutral atmosphere after which the calcined ma terial was removed from the furnace and allowed to cool inair. i

Table 2 which follows shows the average temperatures maintained for the 15-minute calcination periods. Screen analyses were made of each These samples were then used in the grindability tests now to be described.

Table 2.--Aoe"rage temperatures in degreesFahrenheit for fifteen minute caicination periods Desired calcination Soda Potash temperature Aphte feldspar feldspar Quartz Grinda bility tests Samples of the various materials were used in a series of grindability tests based on the method of Bond and Maxson to determine the relative grindabilities of the four uncalcined materials and to determine the eifect of calcinationupon their grinding characteristics.

The grinding characteristics of the samples were shown by the grindability index which is the number of grams of finished material through a given mesh produced per revolution of a ball mill. In this work, 16 mesh was. taken. as the Table 3.Grindability indices of calcined and uncaloined samples and percentage increase in grindability index owing to calcination Percetage Calcination Grindability increase in Material temperature, index, grams grindability degrees F. per revolution index owing to caleination 2. 104 100 l, 000 2. 660 126 l, 300 3. 650. 173 1, 500 3. 406 162 l, 650 10. 380 493 1, 800 9. 934 472 2, 000 10. 313 490 2, 150 5. 248 249 4. 617 100 1, 000 4. 719 102 1, 500 (i. 594 143 1, 650 8.961 194 1, 800 9.001 195 2, 000 8. 480 184 2, 150 5. 538 120 5.060 100 1, 000 5. 174 102 1, 300 5. 352 106 1, 500 5. 799 115 l, 650 6. 249 123 l, 800 7. 295 144 2, 000 7. 149 141 2, 150 5 5. 930 117 3.224 110 1,000 3. 362 104 l, 300 4. 092 127 l, 500' 4. 450 133 1, 650 4. 420 137 l, 800 4. 326 134 2, 000 4. 330 134 2, 150 5. 139 159 1 Uncaleined.

The same results are presented in graphical form in Figure 2 where grindability index is plotted against calcination temperatures. This figure shows that in an uncalcined condition aplite is the hardest to grind, followed in order by quartz, soda feldspar, and potash feldspar. When calcined at 1000 Fahrenheit, aplite alone shows a slight increase in grindability. Between 1000 Fahrenheit and 1300 Fahrenheit there is an increase in the grindability of the quartz, agreeing with the dilatometer data which showed the inversion from alpha to beta quartz at about 1100 Fahrenheit. In the same temperature range the aplite curve practically parallels the quartz curve, and there is very little improvement in the grindability of potash feldspar. There was not sufficient soda feldspar to make calcination tests at all temperatures, and a test at a temperature of 1300 Fahrenheit was omitted.

, At 1650 Fahrenheit, there'is an increase in the grindability of all of the materials except quartz which remains practically constant through the range 1500 to 2000 Fahrenheit. This is conclusive evidence that heating quartz beyond 1500 Fahrenheit does not materiallyimprove its grindability, and it cannot be responsible for the increased grindability of aplite between 1650 and 2000 Fahrenheit, which is unusually marked and agrees with the transition temperature at which permanent deformation takes place as shown by the dilatometer data. From Figure 2 one might be led to believe that the two feldspars were responsible for the increased grindability of aplite in this temperature range. In order to show more clearly the differences in the grinding characteristics, Figure 3 is given.

In Figure 3, the percentage increase in grindability is plotted against calcining temperature. This figure shows that in comparison with the uncalcined materials, the grindability of aplite calcined between 1650 and 2000 Fahrenheit is increased 500 per cent. For the same calcination temperature range, the grindability of soda feldspar is increased only 200 per cent, and the grindability of quartz and potash feldspar, only 150 per cent. Figure 3 shows that the percentage increase in grindability is so much greater for aplite than for any of the other materials that they cannot account for this characteristic inaplite.

Referring again to the data in Figure 2 it shows that although aplite was the hardest to grind in the uncalcined condition, it was the easiest to grind after calcination inthe range of 1650" to 2000 Fahrenheit.

Size composition of grindability samples It may be thought that calcination alone Without grinding would account for an appreciable increase in the fines found in the grindability samples. That this is not the case is shown in Tables 4, 5, 6 and 'l, which follow, which give the screen size distribution of products after calcination but prior to grinding for aplite, soda feldspar, potash feldspar and quartz, respectively.

Table 4.-Size distribution of aplite samples after calcination but prior ta grinding Uncalcined 1000 F. 1300 F. 1500 F. 1650 F. 1300 F. 2000 F. 2150 F. Mesh Size Wt. Cumul. Wt. Cumnl. Wt Oumul. Wt. Cumul. Wt. Oumul. Wt. Cumul. Wt. Oumul. Wt Oumul.

% wt. wt. wt. wt. wt. Wt. wt. wt.

Under the polarizing microscope; it is apparent that the toughness of aplite may be accounted for by its massive crystalline structure and the absence of cleavage or other natural fracture planes The photomicrograph reproduced in Figure '7, which is the same field as that reproduced in Figure 8except that it was photographed without crossed nicols, shows this clearly in that the grain boundaries are almost extinct. Even at 3401 magnifications only a very few fractures at the grain boundaries are noticeable and their width does not exceed two microns. Consequently, combining the knowledge ofthe hardness of the minerals present in aplite and the physical structure of aplite, it is understandable whythe uncalcined aplite is difiicult to grind.

Figures 9, 10, 11, 12, 13, 14, 15 and 16 present photomicrographs ofthe calcined aplite samples. Those calcined to temperatures of 1000, 1300 and 1500 Fahrenheit have an appearance similar to the uncalcined sample and nearly the same grindabilitiese The samples calcined at 1650, 1800 and2000 Fahrenheit showthe presence of numerous fissures andcracks throughout the grains and along the grain boundaries. The boundary fissures are the most pronounced, and in the main, vary from 15 to 180 microns in width but somexas wide as 300 microns were seen. The photomicrcgraphs of the specimen calcined at 1650 Fahrenheit show the coarse preferential fissuringaround the grains and is probably more typical thanthe photomicrographs of the sections calcined to 1800 and 2000 Fahrenheit which show the finer fissuring throughthe large grains of feldspar present in the .aplite rock.

The extensive fissuring just cited for the calcination range 1650 to 2000 Fahrenheit indicates that the expansion was great and agrees with the dilatometer data presented in Figure 1 and the grindabilityindices plotted in Figure 2. Thefissuring displayed in the aplite section calcined at 2150 Fahrenheit is not so pronounced and sharp as in the photomicrographs just discussed. The reason is best illustrated. by the photomicrograph of the same field without crossed nicols which shows that most of the black lines are isotropic glass and not fissures. Recall that at this temperature the aplite became soft during calcination.- Thus the fissures opened up by calcining in the temperature range 1650 to 2000 Fahrenheit are filled with glass when the material is further calcined to 2150 Fahrenheit. This accounts for the rapid drop in grindability at this temperature.

' The photomicrographs explain the percentage change in size distribution caused by calcination which is also illustrated by Figure 6. The reason for the marked increase in minus 16 plus 100- mesh sizes for calcined aplite is that the fissuring caused by calcination is preferentially at the grain boundaries and the average grain size of aplite is 28-mesh. Uncalcined aplite contains no fissures to speak of.

Specific gravity determinations In order to express quantitatively the magnitude of expansion caused by calcination, specific yugravity determinations were made.- 100. minus A inch plus G-mesh particles of each material Were used and the determinations were made by desliming the solids in water, weighing in water,

drying and weighing in air. Table 13 shows the data for uncalcined and 1800 Fahrenheit calcined samples. The aplite is the only sample displaying noticeably a, change in specific gravity indicating expansion, which again verifies the dilatation and grindability data.

Table 13.-Specific gravities of calcined and 1m- Icalcined samples of aplite, soda feldspar, pot ash feldspar, and quartz 1 Specific gravities Material O i i alcincd at Uncalcmed 18000 F Quartz .e 2. 65 2. 64

Water quenching} As previously indicated, it is desirable to water quench the aplite immediately after calcining. This results in greater thermal cracking and fracture of the aplite than when it is air-dried as in the previously discussed tests. In order to determine the effect of water-quenching after calcining, the following tests were made.

I took lumps of aplite, from two to three inches in diameter, and calcined the aplite at a tern perature of about 175035. for a period of minutes. Part of these lumps were then quenched in water and the other part was cooled in air. I then selected samples of the untreated aplite, samples of the treated and water quenched aplite and samples of the treated and air-cooled aplite and made crushing tests on these various samples. Great difiiculty was encountered in crushing the untreated aplite. On the other hand, the treated and air-cooled aplite crushed easily and the treated and water quenched aplite even more easily.

In further tests relative to this invention, samples of the untreated aplite and samples of aplite treated in the manner indicated above and waterquenched were ground in such a manner that all particles would pass through a 16-mesh screen. It was found that in the case of the untreated ground aplite 38% of the ground material passed through a ZOO-mesh screen, or in other words, 38% of the material was in the form of excessive fines. On the other hand, in the case of the treated water-quenched aplite, only 5% of the Table 14.-Capdcities obtained when dry grinding dz'fierently treated aplite in a rod mill under standard conditions gfi gg i Weight Weight Weight Weight ml feedg per cent of per cent of per cent of per cent Test conditions (mud to -2048M 48100M .100200M of -200M g in ground in ground in ground in ground mesh product product product product Aplite calcined at 1800 F. for one-half hour, Water quenched, and dry ground 75. 2 45. 7 24. 9 12. '8 16. 6 Aplite calcined at 1800 1. for onehalf hour, air cooled, and dry ground 50.1 51. 9 20. 8 11.1 16. 2

These tests definitely proved that waterquenching of the aplite after calcining is desirable.

Conclusion increases its grindability to minus l6-mesh, 500

per cent and improves the desirable screen size composition of the ground product, minus 16 plus 100-mesh, by 150 per cent.

3. On being heated from 1650 to l800 Fahrenheit, aplite passes through a transition point and permanent deformation takes place. The deformation is one of expansion and is characterized by the formation of large fissures along the grain boundaries and to a lesser extent across the mineral constituents of aplite.

4. The tests show that the results obtained by calcining aplite within its critical temperature range are caused by properties characteristic of aplite and not accountable forby soda feldspar, potash feldspar and quartz.

5. Water-quenching the aplite after calcining will increase its grindability further beyond that produced by air-quenching and will result in the production of a greateramount "of material of the-proper screen size. 7

6. Calcining and grinding the aplite in the manner described will facilitate acid leaching to reduce the iron content in the manner described in Brenner and Dubble Patent No. 2,304,440, and will also facilitate magnetic separation.

Various other advantages will be apparent.

Havin thus described my invention, what I claim is:

1. The method of treating aplite to reduce it to a grain size suitable for use in ceramic ware or for similar purposes, which comprises calcining lumps of the aplite at a temperature sufficient to cause permanent expansion thereof, said temperature ranging from 1650 Fahrenheit to 2000 Fahrenheit, and then grinding the calcined lump aplite to a size such that all the ground material will pass through a 16-mesh screen while having approximately per cent of the total weight of the ground material greater than mesh.

2. The method of treating aplite to obtain a product having a-maximum particle size of -16 mesh and having more than approximately 80 per cent of the total weight greater than 100 mesh, said method comprising heating the aplite to a. temperature between 1650 F. and 2150 R, cooling, and grinding so that substantially all of the said aplite will pass through a -16 mesh screen while having approximately 80 per cent of the total weight of the ground material greater than 100 mesh.

RALPH F. BRENNER.

CERTIFICATE OF CORRECTION.

Patent No. 2,387,56 October 25, I915,

RALPH F. BRENNER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows Page 5, Table 8, third column thereof, for the numeral "LL22" read L1.5.2 and that the ,sai d Letters Patent should be read with this correction therein that the same may cohform to the record of the case in the Patent Office.

Sighedand sealed this 29th day of January, A. D. 19%.

Leslie Frazer (Seal) First Assistant Commissioner of Patents.

Images