Vol. 19, No. 7
INDUSTRIAL AND ENGINEERING CHENISTRY
816
+
The total yield per hour is 79.4 40.0 = 119.4 grams. With a rate of flow of 150 cc. a minute, the time of contact is 44 minutes. The value of a~ AW X 10-3 = 16.10 e0.0178t where
from Figure 8 is AS = 35.23 and - = AW
*tV X AS
n
--
a
1
= ZD
4 ( ; ):
=
dT
or a
40 = 3262 sq. cm. 0.0503 X 0.2436
142.1
At this temperature 10-3 = 15.91 eO.o17@= 34.84
-A S-
AW-
0.03484
-
0'0928 = 0.0822 2
0.20066
2
n = -5.99 4 eW5.Q9= 1.92 7r
Similarly, 14- and 20-mesh values are figured.
The total surface for the total product is 6514 sq. em. for 119.4 grams. Similarly, the surface of the final product could be figured for a second change in concentration over the next length of crystallizer. This would occur at 30.7" C. for the second 0.300 gram concentration change. Yield in grams would be 322.2 150 X 60 X 1.294 X 0.3 X - = 79.3 grams per hour
and
=
-a
For example, on 10 mesh
- 28.38
The surface generated under these conditions will be 79.4 X 28.38 = 2252 sq. cm. The initial surface was
AW X AS
e
= 28.70
+
Then 28.7 X 79.3 = 2280 sq. cm. The total is 6514 2280 = 8794 sq. cm. for 198.7 grams, or 4420 per 100 grams of product. The average diameter would be 198'7 = 8794, D = 198'7 = 0.0928 cm. 8794 X 0.2436 D X 0.2436 Approximate values for the first three screen sizes may be calculated by the aid of the probability equation:
MESH 10 14 20 28 35
OPENING Cm. 0.2006 0.1410 0.1000
n 1.92 19.66 42.80
SCREEN AREAPER TEST GRAX Per cent CC. 2.0 X 20.46 X 29.14 = 20.0 43.0 X 41.03 30.04 X 57.73 = 81.61 = 4.0" X
-
TOTAL SURFACE
cc.
40.8 682.0 1762.0 1730.0 326.0
4440.8 From actual tests 28-mesh material is about one-half that of 14 20 mesh, and the amount of 35-mesh is the remainder or 4 per cent. a
+
The surface of the calculated product is within 1 per cent of the required and the amount on any one screen would be within a few per cent of the expected values. QUAKTITATIVE DATA-It is very significant that quantitative measurements showing the relation between the weight of material crystallized and the new surface generated have been made and further that these results are consistent with each other, within a range of reasonable experimental error. Previous work in this field has been confined to a study of comparatively large individual crystals.
Estimation of Very Small Amounts of Yellow Phosphorus in Red Phosphorus' By Raymond H. Kray U. S. N. POWDER FACTORY, INDIANHEAD,MD.
HIS method is based on the reaction between copper
T
sulfate and a carbon disulfide solution of yellow phosphorus. If a piece of paper impregnated with copper sulfate is dipped into a solution of carbon disulfide containing yellow phosphorus and then quickly dried, the copper phosphide and metallic copper formed color the paper brown, the depth of this color depending on the amount of yellow phosphorus in the solution. PREPARATION OF TESTPAPER-Ten grams of copper sulfate are dissolved in 100 cc. of distilled water. Pieces of filter paper (Schleicher & Schull No. 589 has proved satisfactory) are dipped into this solution, drained off and allowed to dry in air. The dried paper is cut into strips about 0.6 by 10 cm. PREPARATIOK OF STANDARDS-Asolution containing approximately 0.5 gram of yellow phosphorus per 100 cc. of carbon disulfide is made up. By diluting this solution a series of permanent standards can be made up; the lowest containing 0.00015 gram and the highest 0.0010 gram of phosphorus per cubic centimeter of solution make a convenient working strength. About eight or ten of these bottles kept in the dark are the standards for comparison. METHODOF ANALYsIs-Twenty grams of the red phosphorus are treated with 30 cc. of carbon disulfide in a flask having a ground-glass stopper. After shaking up and thoroughly mixing it is filtered and 15 cc. of the filtrate or onehalf of the carbon disulfide content taken. This is tested with the copper sulfate paper. If the concentration of yellow 1 Received
partment.
April 8, 1927. Published by permission of the Navy De-
phosphorus is not high enough to make comparison, the solution is evaporated on the steam bath, and measured and tested out at different stages during its concentration. I n this way stains produced on the test papers are compared with the other test papers immersed in the standard solutions and the exact concentration of yellow phosphorus in the unknown solution is determined. After determining the total phosphorus in the 15 cc. of solvent, it is multiplied by 2, since this only represents half the sample. By filtering off the carbon disulfide immediately the method is made very rapid and serves as a good comparative test for yellow phosphorus. But the actual results obtained are low. This was shown by treating a sample by the above method, adding fresh quantities of carbon disulfide and allowing to stand overnight. About one-third more yellow phosphorus was leached out and shown to be present, by the additional treatment. A more exact method, and the one always used when accuracy is demanded, is to grind 20 grams of the red phosphorus under carbon disulfide and then quickly transfer the mixture to a glass-stoppered flask and allow to stand for 24 hours in the dark. Filter and wash thoroughly with carbon disulfide, making the filtrate and washings up to 100 cc. in a glass-stoppered measuring cylinder. This solution can be evaporated, so that its concentration of yellow phosphorus can be determined by the method given above. This method is practical down to 0.003 per cent yellow phosphorus, using indicator paper as described. Comparison of stains is made more delicate by viewing the translucent test paper through a strong light, preferably bright daylight.
