T H E J O U R S A L OF I L V D C ‘ S T R I A L A-1-D EA\7GINEERIMG C H E M I S T R Y
168
Dark colored sugar solutions naturally tend to purify the light but with light colored solutions there is little purification. When these blue and violet rays are not cut off the polarization is always higher than when they are removed. I n some cases a n increase of as much as 0 . 3 ~V. has been noted. Schonrockl noted a n average increase with some observers of O . I Z j o V. He recommends as a filter a 6 per cent. solution of bichromate in a cell I I / ~ cm. long. Browne* found t h a t the average difference between t h e readings of the lowest of, 4 observers, when using a 3 per cent. solution in a 3 cm. column, was 0.03’ V. while with no cell i t was 0 . 2 2 ~V. and with a I per cent. solution in a 3 cm. cell i t was 0 . 0 8 ~V. From this it is seen t h a t results are made concordant by the use of a 3 per cent. solution in a 3 cm. column or by using a solution of such strength t h a t the percentage multiplied by the length in centimeters is 9. Most makers of polariscopes include in their apparatus either a light filter cell or a crystal of bichromate placed in the ocular but in their directions accompanying the instruments no particular mention is made of the use of the cell. Letters addressed to foreign sugar chemists regarding the use of a light filter cell brought the following replies. Dr. A. Herzfeld, of the Institute for Sugar Industry, Berlin, Germany, writes : “The bichromate filters in small tubes were introduced by me more than twenty years ago and t h a t first in the Peters’ instrument and later they were taken up by Schmidt and Haensch. They are not absolutely necessary in the investigation of colored sugar products by means of the half shadow instrument b u t they are absolutely necessary in the case of colorless sugar solutions. We use a I ’ / ~ cm. layer of a 6 per cent. bichromate solution. We remove the bichromate solution from the apparatus only in case very dark solutions are being examined in which i t is just possible to adjust to a half shadow. I believe t h a t the use of the ray filter cannot be avoided in electric or acetylene lights with colorless sugar solutions. A solution is always t o be preferred over solid crystals, since i t can easily be removed or renewed.” Dr. F. Strohmer, of the Chemical-Technical Experiment Station for the Austrian Beet Sugar Industry, Vienna, Austria, writes: “We always use a bichromate cell in our polarization apparatus which is placed between the polarization apparatus and the * We have always had the best success source of light. with this arrangement and no differences a t all have ever occurred. As a source of light we use a strong Auer or Nernst light and with such mixed lights I consider this arrangement necessary since by means of i t the light, which is finally polarized, is homogenized.” Mr. H. C. Prinsen-Geerligs, of Amsterdam, Holland, writes : “The two hundred odd sugar laboratories in Java are organized and have the following rule: I ‘ ‘When moving the screw for the exact quality of color, the difficulty is often encountered t h a t a t the equal shading of the two halves of the discs, the color of both is not exactly the same, one-half possessing a red and the other a blue tinge. This very troublesome phenomenon, which hinders the exact ascertaining of the proper equality, is especially met with in the case of colorless or feebly colored solutions having t o be polarized and is due t o small differences in the optical properties of sucrose and quartz. I n the old apparatus this trouble was neutralized by inserting a plate of transparent potassium bichromate in the ocular which absorbs the blue and violet rays and imparts a yellow color to the disc. In modern apparatus the plate is replaced by a solution of bichromate which is poured in a short observation tube of a very wide diameter which is inserted in the polariscope between the lamp and the lens and which may
***
* *
2
Ztg. Ver. d . Zuckerird., 64, 521-58 (1904). U.S . Dept. Agr., Bur. Chem.. Bull. 122, p. 222.
Feb., 1913
be taken out t o be made afresh. Working with sources of white light, i. e., unfiltered electrical, Argand, Auer, kerosene and acetylene light, every separate observer finds values which are identical for his eye but which after experiments made by Schonrock may differ by 0.008 to 0 . 1 2 7 ~V. with those obtained by other operators when the polarizations are about 100,which clearly shows that by no means polarizations should be made withLunfiltered white light. These differences disappear well nigh entirely if the light from the above mentioned sources is purified by allowing i t t o pass through a 6 per cent. solution of potassium bichromate in a layer of 6 cm. Hereby the difference in color between the two halves of the disc after the fixing of the just position, which is caused by the difference in dispersion between sucrose and quartz, is almost totally neutralized. In order to obtain by different operators fully concording figures, it is indispensable to apply the aforementioned tube with potassium bichromate solution. Only in case the polariscope is not equipped with such a contrivance a plate of bichromate is to be inserted in the ocular. When polarizing dark colored solutions, the bichromate solution may be more diluted but it should never be left out.’ “You see we are rather strict in Java.” Dr. H . Pellet, of Paris, France, writes: “For the saccharimeter of the Schmidt and Haensch kind, it is necessary to use a light, slightly colored yellow by means of a cell of bichromate of potash more or less concentrated.” Dr. C. Fischma, member of the Board of Directors of the AllRussian Sugar Association, Kiebr, Russia, writes : “We in Russia have no legal regulations concerning the use of bichromate of potash in sugar determination by polarizing. I n the Association laboratory, however, a 5 per cent. solution of bichromate of potash is always used for the polarization of white sugar because it makes possible much more accurate polarization. In the polarization of yellow sugars, massecuites and molasses this laboratory does not use this solution.” Dr. Hugh Main, of London, England, writes: “It is easier to read colorless solutions with a bichromate solution in the polariscope than without it and, therefore, I use it in testing the polariscope with pure sugar and retain i t in position for all other polarizations.” In defining the 100 point of the Ventzke scale, the Imperial Reichsanstalt of Germany and the United States Bureau of Standards have adopted the use of this light filter cell. I recommend, therefore, to this Commission the following resolution : That where white light is used in polarizations, the same shall be filtered through a neutral bichromate of potash solution of such a strength t h a t the per cent. composition multiplied by the length of column in centimeters be 9.‘ A. HUGHBRYAN SUGAR LABORATORY, BUREAU O F CHEMISTRY LT. S . DEPT.O F AGRICULTURE
THE ANALYSIS OF UNSWEETENED EVAPORATED MILK. Editor Journal of the Industrial and Engineering Chemistry: We have had considerable difficulty in the fat determination of unsweetened evaporated milk by the Babcock method. To obtain good results directly on the milk, without modification in the manipulation, is a n impossibility. Working on the diluted sample does not give satisfactory results. The Gottlieb method gives fair results, but it has been shown’ that these results are uniformly low. The method advocated by the Indiana Experiment Station in Bulletin 134 gives good results, but they are not always uniform, much depending upon the milk with which one is dealing. The amount of acid, 1 7 . 6 cc., given in the method is too much in many cases. The Commission unanimously adopted this resolution September 10. in New York City. 2 Indiana Expt. Sta., Bull. 134. 1
1912, at its Meeting
The following method, we have found, gives uniformly good results on all kinds of unsweetened evaporated milk. I. MIXING THE SAMPLE The sample is mixed by shaking, pouring and stirring; some globules of fat persist in staying unmixed;. by looking across the surface of the milk with the eye in such a position that the light is reflected to it from the milk, one can easily detect these small chunks of fat and see whether the sample is homogeneous. If these chunks of fat will not mix, warming slightly (not over 40° C.) will help, or sometimes a sample will be met with that needs a very small pinch of caustic soda to aid in emulsifying the fat. 11. FAT Weigh 4 . 5 grams of the well mixed sample into a IO per cent. Babcock milk bottle. Add commercial sulfuric acid (sp. gr. about 1.8) of the same temperature, mixing the two with a whirling motion until a dark chocolate color is produced. From six to eight cubic centimeters of acid are usually necessary. Place the bottles in boiling water and heat for from fifteen to twenty minutes. Remove and let stand until nearly cold. Fill the bottle two-thirds full of hot dilute sulfuric acid ( I volume of water to I volume of the concentrated acid), and mix well. Place in the centrifuge and whirl five minutes. Fill to neck with hot half-strength sulfuric acid and whirl three minutes. Add hot water to bring the fat column into the neck of the bottle and whirl two minutes. Read a t 1 2 0 O F. to 125O F. from the bottom of the column to the extreme top of the meniscus. The reading multiplied by four gives the percentage of fat. NOTES ON THE METHOD I . I n the coudensing process the casein becomes toughened so that it is extremely difficult to get it dissolved in the sulfuric acid. The heating in the bottle with the sulfuric acid, and subsequent standing, aids in this process. There is little danger of charring if the correct amount of sulfuric acid is added. 2. If hot water is added before whirling, in most cases a precipitate forms which interferes with the determination. The addition of half-strength sulfuric acid prevents this. 3. Four and one-half grams were found to be the best amount with which to work. 4. The results obtained by this method have been very gratifying, giving uniformly good, clear readings that check well. 111. TOTAL SOLIDS
Weigh I gram of the well mixed milk into a tared aluminum milk dish. Add 25 cc. of water and evaporate to dryness on the steam or water bath. Dry to constant weight in a steam or water oven. This method was found more satisfactory than making up a diluted sample of known strength and obtaining the sample for solids from it. I t is simple and easy to manipulate. C. A. A. UTT’ KANSAS STATE AGRICULTURALCOLLEGE
there is a variation of I . 58 per cent. between the highest and the lowest. A rule should be so expressed that if it is followed good results must follow. It is not enough that good results m a y follow. I t is, to say the least, conceivable that there would be greater difference of conditions in any two given laboratories than prevailed in my laboratory a t the time when the Fletcher burner was burning and when it was not. Percentage volatile NO.
1
Very little g a s . .
h-0. 2
More gas t h a n No. 1 . . . . . . . . . . . . . . . . .
So. 3
Slight increase of gas over No. 2..
So. 4
More gas t h a n S o . 3 . . . . . . . . . . . . . . . . .
No. 5
No. 6
Assistant Chemist Kansas S t a t e Board of Health.
21.70 122.17
air.. . . . . . . . .
I n my regular work I have always used a three-tube compound burner and have never had any difficulty in getting results agreeing within 0 .2 per cent., the average difference between duplicates being 0 . I per cent. By my method the foregoing coal showed 2 2 . 6 7 per cent. and 2 2 . 5 7 per cent. I had attributed the close agreement of my results to the fact that all the coals which came inder my observation were high-grade steam coals, New River or Pocahontas. I now believe that my method is, in part a t least, responsible. I t is noticeable that as the results approach the limit, the agreement becomes better and it seems not unreasonable to infer that it is easier to get results when all the volatile matter is driven off than to stop a t some point short of that result. I am aware that the phrase “all the volatile matter” sounds loose and unscientific, but the following determinations show that there is a point not easily overstepped to which that definition may be applied. The same coal was heated for increasing lengths of time according to my method, with the following results: Percentage volatile (22.64
8 minutes.. .
. . . . . . . . . . . . . . . . . . . . 7. 22.55 9 minutes., . . . . . . . . . . . . . . . . . . . . . . . 22.53 10 minutes.. . . . . . . . . . . . . . . . . . . . . . .
.22.85
Applied to a n anthracite coal, my method gave the following results: Percentage volatile 7 minutes..
..........
8 minutes.. 9 minutes..
.... ...
5 .OO
..
5.02 5
.oo
Applied to a gas coal, the results were: Percentage volatile 7 minutes.
Much interesting and ingenious work has been done during the last two or three years on the determination of “volatile” in coal. I t seems to me that his work is mistaken in that it attempts to patch up a n inherently faulty method. The following determinations illustrate the weak point in the method. These determinations were all made by the “official” method except that the flame was protected, and a Tyrell burner and a pipe clay triangle with projections were used. I n every case the flame was over 20 cm. in height and a good non-smoking flame. I n No. 2 a Fletcher burner was burning on the same gas pipe as the determination but was put out before No. 3 was started; the regulators of gas and air on the burner were in the same position in each case. Here are a number of analyses made with ordinary care, all complying, except as noted, with official directions and yet
,,, , ,
20.90 21.20
{ { 2’:s” Burner pushed t o its u t m o s t . . . . . . . . . . 2 2 . 3 0 { 22.48 Same gas as No. 4-more
MASHATTAN,Sept. 18, 1912
THE DETERMINATION OF “VOLATILE” I N COAL Editor of the Journal of Industrial and Engineering Chemistry:
.f
....................
7.31 :. . . . . . . . . . . . . . . . . . . . . . . { 337.48
8 minutes.. .......................
37.58
The slightly higher results which my method gives were not due to entrainment of solid particles. Both determinations Percentage ash gave : Official method. ...................... 4,40 I n sample heated t e n minutes.. . . . . . . . . . 5 . 4 5
One thing that has been impressed on me during these experiments is the difficulty of judging, and consequently, defining, the heating power of a flame. I determined the first coal, a New River coal, and the anthracite with a n ordinary Bunsen burner which I expected would give very low results. I obtained: Percentage volatile 21.60 S e w River coal. . . . . . . . . . Anthracite.
.............
21.65 4.T5 4 60 4.85
I tried determinations on these coals with the addition of
