T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
138
111-In addition t o the puncture test, the Webb machine may be used for tensile tests, elongation tests, and compression tests. The tensile test, especially when “across the grain,” is a n important index of the value of a fiber box as a shipping container. This “across the grain” value may also be found more quickly by a puncture test, using the “wedge” plunger. IV-The pocket-size model makes i t possible t o test corrugated boxes under conditions which are impossible a t present. V-Besides corrugated products, the Webb machine can be used for testing many other flat substances, such as paper, cardboard, * “solid fiber” boards, gummed tape, fabrics, etc.
By W. D. COLLINSAND W. F. CLARKE Received July 25, 1918
Soon after the outbreak of the present war, difficulty was experienced in obtaining pharmaceutical zinc oxide which would meet the requirements of the Ulzited States Pharmacopoeia. When the matter was first considered, the statement was made t h a t zinc oxide of the required purity was very easy t o obtain. It was even stated t h a t material bought for use as a pigment in painting might be more nearly free from lead than a certain sample of pharmaceutical zinc oxide which contained about 0 . 2 per cent of lead. Mr. C. L. Black of the Philadelphia Station of the Bureau of Chemistry reported in May 1917 t h a t analysis of such samples of zinc oxide as could be procured on the market a t t h a t time indicated t h a t practically all the zinc oxide obtainable contained more lead than was permitted by the U . S. P . test. Some manufacturers a t this time stated on the labels t h a t the zinc oxide sold by them contained heavy metals slightly in excess of the U . S . P. limit. Prof. C . H. La Wall’ published an article calling attention t o this matter and made the suggestion t h a t all samples of pharmaceutical zinc oxide should be tested for lead. I n order t o learn whether it would be possible t o obtain zinc oxide reasonably free from lead, samples were obtained on the market and from manufacturers, and the question was taken up with Dealer A B A D
F
B
K
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H I,
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149 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1914 1917 9-26-17
N
135 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136.
8-4- 1 7 8-4-1 7
0
.................................
KO.2
TEST
F O R LEAD I N ZINC O X I D E BY T H E U. S . P. T E S T F O R H E A V Y MET\ALS
LEAD IN PHARMACEUTICAL ZINC OXIDE
Received NO. 1-13-17 117 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-16-17 1-16-17 119... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84-17 133.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4-1 7 134... 8-6- 1 7 137 . . . 1915 130.., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-27-1 7 148... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-28-17 158... ............................... 11-29-17 1 5 9 . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-5-17 1 5 5 . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1-18 1 7 8 . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4- 18 187.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11,
the U. S. Geological Survey and with manufacturers of zinc oxide. It was learned from Mr. C. E. Siebenthal of the U. S. Geological Survey t h a t one company producing zinc in the United States owned a mine which contained no lead minerals and, therefore, should be able t o produce zinc oxide free from lead. It would seem probable t h a t zinc oxide made from electrolytic zinc should be free from lead. It was learned from manufacturers t h a t zinc oxide was being made according t o both of these principles, and t h a t the products contained much less lead than the amount necessary t o respond t o the U . S. P. test for heavy metals.
MELLONINSTITUTBOB INDUSTRIAL RESEARCH OF PITTSBURGH. PITTSBURGH, PA. UNIVERSITY
SAMPLE
Val.
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P
I n order t o determine the sensitiveness of the U . S. P. test for lead in zinc oxide, two series of experiments were conducted entirely independently in order t o establish the limits of sensitiveness. Different quantities of lead from a solution of lead nitrate were made up with zinc oxide and hydrochloric acid so as t o give the concentrations of zinc and acid prescribed by the U.’S. P. for the test for heavy metals. I n one series of tests (W. F. C.), the hydrogen sulfide used was made according t o the directions of the P h a r m a copoeia. I n the other series of tests (W. D. the hydrogen sulfide used was prepared in the ordinary manner by the use of hydrochloric acid and ferrous sulfide and the gas was washed through water. No difference could be detectcd in the results by the two methods. It was found t h a t a sample of zinc oxide might contain as much as 0.05 per cent lead and fail t o respond t o the test for heavy metals. I n some cases the test would be obtained and in others it would fail. When the sample contained as much as 0.I per cent, a positive test was always obtained and with any amount greater than 0.05 per cent there was rarely any doubt about the response t o the test.
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SAMPLES
A number of samples of zinc oxide were purchased a t various drug stores. Some samples were furnished by manufacturers and others were obtained from dealers through the regular purchasing office of the Bureau.
TABLEI-ZINC OXIDE Producer or Lead Per cent Manufacturer ? 0.25 0.036 0.25 0.19 E G 0.19 C 0.26 0.041 H 0.006 I 0.004 I I 0.008 0.013 K I 0.004 0.008 I METALLIC ZINC M 0.026 M probably 0.094 K 0.012 PIGMENTZINCOXIDE 0.13 53.2
d
....
u. s. P. Test
0 0
Remarks Purchased at local drug store Purchased at local drug store Purchased at local drug store Purchased at local drug store Purchased at local drug store Purchased a t local drug store From Bureau stock of reagents Show sample from office of manufacturer Sample sent by manufacturer Sample sent by manufacturer Purchased by Bureau Supply Office Purchased by Bureau Supply Office Purchased by Bureau Supply Office
.. .. ..
Analysis on label lead 0.01 per cent Analysis on label: lead none Sample furnished by manufacturer
+ 0 f
++
0 0 0 0
0
Trace Heavy
About 22 per cent barium sulfate
1 Am. J. Phaum., 89 (1917), 353-5. In a later article (Ibid., 90 (1918), 499). Professor La Wall notes that U . S.P. zinc oxide is now on the market. H e proposes tests for lead which will detect 0.03 per cent PbO in zincoxide, while the present U . S. P test under the best conditions will detect 0.05 per cent.
Feb.,
1919
*39
T H E JOURiYAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Samples of zinc oxide were also purchased a t two paint stores. A few samples of metallic zinc were examinedfor their content of lead. NETHOD O F ANALYSIS
Lead was determined by t h e well-known method of separating as sulfate and weighing as chromate. From 5 t o 40 g. of zinc oxide or zinc were dissolved in water and sulfuric acid, with a slight excess of acid. The volume was usually about I O O cc. for I O g. of zinc oxide. Alcohol ( g j per cent) was added in quantity just short of t h a t necessary t o start precipitation of the zinc sulfate, usually making about one-third of the final volume. The solution was allowed to stand over night; the lead sulfate was filtered off on asbestos, washed with 50 per cent alcohol, and dissolved in ammonium acetate. The lead was reprecipitated as chromate, after acidifying with acetic acid, by adding potassium dichromate solution. After standing over night, the lead chromate was filtered on asbestos in a weighed Gooch crucible, dried to constant weight a t IIO', and weighed. The accompanying table gives descriptions of the samples and t h e results obtained for lead, and also the results of testing according t o the United States Phaymacopoeia. SUM lLlA R Y
For a short time after the beginning of the war it was n o t possible t o procure zinc oxide of the U . S. P. standard produced in the United States. The U . S.P. test for heavy metals will not detect less than 0.0; per cent of lead in zinc oxide. It is possible a t the present time t o obtain zinc oxide which, with respect t o the presence of lead, is of much higher quality than is called for by the requirements of the U . S. P .
these troubles are aggravated since the precipitate and liquid tend t o creep under t h e paper filter, especially if continuous vacuum is not maintained, thus requiriqg a second filtration. I
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BUREAUOF CHEMISTRY
U
s. DEPARTMENT O F AGRICULTURE D. C. WASHINGTON,
AN EFFICIENT LABORATORY FUNNEL FOR FILTERING NEUTRAL LIQUIDS, ESPECIALLY THE VOLATILE ORGANIC SOLVENTS B y T. E. ALDRICH Received October 23, 1918
Those w h o have had occasion in the laboratory t o collect precipitates suspended in ether, chloroform, acetone, alcohol, or mixtures of these organic solvents, especially by forced filtration, have no doubt a t times experienced trouble when using the ordinary funnel and especially the Buchner funnel. I n Ihe case of aqueous solutions, the filter paper, after being moistened and pressed closely to the funnel for the purpose of removing bubbles of air t h a t interfere with filtration, adheres closely to the glass and filtration is ordinarily rapid, while in the case of ether, for example, the solvent being volatile passes away rapidly, and channels and spaces are formed between the paper and the funnel; the paper tending to lift from the glass. This is especially true when filtration is interrupted for a short time; in any case the formation of channels and spaces interferes with rapid filtration. When the Buchner funnel is employed
F I G .1
The advantage of t h e funnel t o be shortly described lies in the fact t h a t the filter paper is clamped securely between two plates by a screw thread so t h a t i t cannot lift even when the filtration is interrupted, a n d thus allow the formation of channels and passages f o r t h e liquid and precipitate underneath. There is no necessity for second filtrations, and a more rapid filtration is also effected by this arrangement.
