October 1, 1920.] 



THE INDIA RUBBER WORLD 



29 



carbon dioxide or helium was about seventeen times the rate at 

 degrees C. The permeability to hydrogen was about twenty- 

 two times as great at 100 degrees as at degrees C. 



6. The relative permeability of rubber to some common gases 

 is shown in the following summary: 



Relative 

 Permeability 

 Gas Hydrogen = 1 



Nitrogen 0.16 



Air 0.22 



Argon 0.26 



Oxygen 0.45 



Helium 0.65 



Hydrogen 1.00 



Carbon dioxide 2.9 



Ammonia 8.0 



Methyl chloride 18.5 



Ethyl chloride 200.O 



7. The permeability of rubber to water vapor is high — approxi- 

 mately fifty times the permeability to hydrogen. This value, not 

 having been determined with any precision, is not included in the 

 table above. 



METHODS OF ANALYSIS 

 THE DETECTION OF NATURAL BARYTES IN LITHOPONE. ETC. 



THE FOLLOWING METHOD has been in use for 22 years in the 

 laboratory of Michael Nairn & Co., Limited, Kirkcaldy, 

 Scotland. It is given as reported by S. Stewart, F. I. C, in the 

 Jountal of the Society of Chemical Induslry, July IS, 1920, 

 page 188t. 



Lithopone, Orr's zinc white, and other pigments composed 

 essentially of zinc sulphide and barium sulphate should contain 

 the latter only in the precipitated form. Inferior qualities some- 

 times contain natural barytes, to the detriment of their covering 

 power, owing to the large size of the particles of barytes as 

 contrasted with those of the precipitated sulphate. Its opacity 

 is less, and although, when used as an ingredient in ordinary 

 paints, this is perhaps of secondary importance, it becomes a 

 matter of serious consideration when used for some other pur- 

 poses ; for example, in making white inlaid linoleum the use 

 of lithopone containing natural barytes leads to the production 

 of a yellowish white. 



The microscope affords a convenient means for differentiating 

 between natural and precipitated barium sulphate. The test is 

 carried out as follows: A minute portion of the sample is 

 spread on a microscope slide with a drop of water, dried, and 

 examined with a !4-inch or V^-inch objective, the diaphragm 

 being closed .so as to give a dark background. If only preci- 

 pitated barium sulphate be present, it appears as a very fine 

 powder composed of minute crystals of uniform size, whereas 

 if there is an admixture of natural barj-tes, even when very 

 finely ground, transparent irregular pieces of greater size will 

 appear. The certainty of the method is enhanced if the zinc 

 sulphide present in the lithopone be first removed by treatment 

 with dilute hydrochloric acid and potassium chlorate and the 

 insoluble residue examined as above. 



TECHNICAL ANALYSIS OF LITHOPONE^ 



TOTAL ZINC AS ZINC SULPHIDE 



Weigh two grams of lithopone into 600 cc. beaker, add a little 

 waier to moisten, and then 20 cc. 1-1 hydrochloric acid. Take 

 to dryness on steam plate, take up in 75 cc. of water, add five 

 cc. of concentrated hydrochloric acid, and seven grams of am- 

 monium chloride, dilute to 350 cc. with hot water, heat to 180 

 degrees F. on steam plate and titrate slowly with potassium 

 ferrocyanide, one cc. of which equals 0.01 gram of zinc, using 

 uranium acetate as externa! indicator. 



ZINC OXIDE 



Weigh 20 grams lithopone into 400-cc. beaker, add 100 cc. of 

 five per cent acetic acid and let stand on the steam plate for two 

 hours, with occasional stirring. Filter into 600 cc. beaker, wash 

 with water, boil to small volume, transfer to porcelain dish and 

 evaporate to dryness. Add 20 cc. 1-1 hydrochloric acid and 

 evaporate again. Take up in water, add five cc. concentrated 

 hydrochloric acid and seven grams ammonium chloride, dilute to 

 350 cc, heat to 180 degrees F. and titrate with potassium ferro- 

 cyanide. Calculate to zinc oxide. 



ACTUAL ZINC SULPHIDE 



From the total zinc substract the zinc found as zinc oxide and 

 calculate difference to zinc sulphide. Total barium as barium 

 sulphate. 



Weigh three grams sample into 250 cc. pyrex beaker, add ten 

 cc. water and ten cc concentrated hydrochloric acid. Take to 

 dryness on steam plate, add 75 cc. water, few drops methyl 

 orange and if not acid add a few drops hydrochloric acid. Boil, 

 filter and wash. Return filter plus precipitate to original beaker, 

 add ten cc. water and five cc. nitric acid. Take to dryness on 

 steam bath, add 30 cc. concentrated sulphuric acid and fume 

 strongly. In case acid is dark in color add crystals of potassium 

 nitrate until colorless. Fume until only a trace of insoluble 

 matter (silica) remains. Cool, dilute to 200 cc, boil, let stand in 

 warm place to settle, filter, wash, ignite and weigh as barium 

 sulphate. Calculate to percentage barium sulphate. 



WATER SOLUBLE SALTS 



Ten grams lithopone are weighed off into a covered 400-cc. 

 beaker, 200 cc. water added, mixture stirred and heated on the 

 steam bath for one to two hours to effect solution of soluble 

 salts. Filter on four-inch Buchner, wash with hot water and 

 evaporate filtrate in porcelain dish. When down to 50 cc. filter 

 through a blue ribbon paper and wash with water. Receive 

 filtrate in a weighed platinum dish, evaporate to dryness on steam 

 bath and then dry at 110 degrees C. for one-half hour. Cool, 

 desiccate and weigh. 



IRON 

 Weigh 20 grams into 400-cc. beaker and moisten with about 

 15 cc. of water, then add SO cc. concentrated hydrochloric acid 

 slowly and with stirring. Let it stand over night, filter, wash 

 with hot water containing hydrochloric acid, oxidize the filtrate 

 vnlh. bromine and precipitate the iron by using a slight excess 

 of ammonia water and allowing to settle several hours. Filter, 

 dissolve and reprecipitate the iron three times. The iron precipi- 

 tate is now ignited and weighed as ferric oxide. 



MANGANESE 



Boil five grams lithopone with 50 cc. 1-1 nitric acid, filter, 

 wash and dilute filtrate to 150 cc. with cold water. Then add a 

 little sodium bismuthate and allow to stand in the cold for 

 twenty minutes. Filter through asbestos pad and compare with 

 standards. 



^J. A. Wyler in the Cliemist- Analyst, 



CHEMICAL PATENTS 

 THE UNITED STATES 



Q PONCE Rubber. Articles such as balls having cells therein, 

 *^ largest at the central portion of the article and decreasing in 

 size toward the surface of the article, may be formed from a 

 mixture of rubber 70, sulphur 6, ammonium carbonate 8, zinc 

 oxide 12, and magnesium oxide 4 parts. (James B. Wishart, 

 Trenton, New Jersey, United States patent No. 1,345,904.) 



Sulphur-Terpene Compound. A sulphur compound which ex- 

 hibits the following characteristics; neutral, amorphous, non- 

 colloidal, insoluble in water, soluble in toluol and xylol and ca- 

 pable of reacting with rubber. (William Beach Pratt, Welleslcy, 

 Massachusetts, assignor to E. H. Clapp Rubber Co., Boston, Mas- 

 sachusetts, United States patent No. 1,349,909.) 



