Jan.,
1920
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 C H E M I S T R Y
cent of the volume taken for distillation. The composition of each of the intermediate fractions is actually determined, and the error introduced by this determination is small, since i t is applied t o only small volumes. The apparatus works well on mixtures containing widely varying percentages of benzene, toluene, and solvent naphtha. FUEL VALUE OF VOLATILE LlQUlD MIXTURES
By George Barsky DEPARTMENTOF CHEMICAL ENGINEERING, COLUMBIA UNIVERSITY, NEW Y O R E CITY Received August 14, 1919
The gasoline substitutes now coming on the market are, in general, mixtures of very volatile with less volatile liquids. When a bomb calorimeter is employed in the usual way t o determine the fuel value of such a mixture, difficulties are encountered. It is extremely difficult t o weigh out a sample owing t o its volatility a n d i t is next t o impossible t o get complete combustion. Attempts t o burn.in the open pan, in glass bulbs, mixed with other materials, and other common modifications did not give satisfactory results with a fuel containing constituents of volatility varying from ether t o kerosene. The difficulties were finally surmounted in a simple way by the use of gelatin capsules of a particular shape. These were constructed of ordinary capsules by turning in the caps so t h a t they fitted the menisci when the capsules were filled. I n this way all the air was excluded. The igniting wire was wound several times around the capsule, which was allowed t o rest in the pan. This modification was very successful, giving results t h a t checked within 60 B. t. u., i. e . , as close as was obtained on solid fuels with the same calorimeter.
r[-]
THE MCCRUDDEN GRAVIMETRIC CALCIUM METHOD MODIFIED
By J. 0. Halverson and J. A. Schulz DEPARTMGNT OF NUTRITION,OHIO AGRICULTURAL EXPERIMENT STATION, * WOOSTGR, OHIO Received July 22, 1919
The results obtained by the substitution of the volumetric asbestos Gooch method for the gravimetric procedure in the McCrudden calcium method have facilitated the determination of the small amounts of calcium which have t o be determined in biological and agricultural products. It is thought these results are of sufficient interest t o warrant their publication. McCruddenl was unable t o employ the Gooch crucible on hardened filter point and suction t o advantage in filtering calcium oxalate. He says: When Gooch crucibles were tried, it was found that thin layers of asbestos did not retain the precipitate. When layers thick enough to retain the precipitate were used, they soon clogged up and prevented passage of the fluid.
The use of i g n i t e d non-reducing asbestos in filtering calcium oxalate would greatly facilitate the estima1
J . B i d . Chem., 10 (1911), 194.
77
tion of small amounts of calcium by the potassium permanganate method rather t h a n by the gravimetric procedure. Therefore if the precipitate and asbestos in the Gooch crucible could be washed into an Erlenmeyer flask it could be heated and titrated a t once with a considerable saving of time. It is apparent from the number of modifications1 proposed from time t o time for the estimation of calcium in feeds and agricultural products t h a t this estimation is not readily done without contamination.2 An occasional contamination with iron occurs in two substances, wheat bran and raw rock phosphate. The proposed modification may also be used as a means 'of eliminating this troublesome iron, which is occasionally occluded by t h e calcium oxalate precipit a t e in the gravimetric procedure, discoloring somewhat the calcium oxide, causing slightly higher results (0 008 per cent). The McCrudden method3 has given good results on both biological and agricultural products for the past two and one-half years and the present modification has been in use during the past year. P R E P A R A T I O N O F THE ASBESTOS-High grade ig?&ed long-fibered asbestos was used. The ignited asbestos was placed in hot sulfuric acid ( I : 5 ) and digested one hour a t 60' t o 70' C., with occasional shaking while adding a few drops of K M n 0 4 , keeping a t a faint pui-ple tint, and the beaker was kept covered. The material was then placed on a Buchner funnel and washed with distilled water containing a faint tint of K M n 0 4 until free of acid. This is preserved for future use free from dust and dirt. P R E P A R A T I O N O F THE G O O C H CRUCIBLE-The Gooch crucibles of moderate thickness which filter readily a t two t o three atmospheres pressure, are prepared with some care, using the treated ignited asbestos of three grades of fineness. The separation into three grades of fineness-very fine, medium, and coarseis done by shaking, decanting, and separating the asbestos in water into three Erlenmeyer flasks. The long, coarse fibers are first used for a foundation, next the medium fibers t o fill the interstices, and finally for a compact top layer, the fine sediment which settles slowly in water. Properly prepared Gooch crucibles4 have given no trouble in filtering precipitates of calcium oxalate. T I T R A T I O N O F THE C A L C I U N OXALATE-After the calcium oxalate precipitate is washed free from oxalate and oxalic acid, the precipitate and pad are transferred with a small quantity of hot water t o an Erlenmeyer flask and titrated immediately a t 6 j C., using sulfuric acid (I : 5 ) . It is well known t h a t the volumetric method is apt t o run slightly lower when the calcium oxalate precipit a t e is washed off the filter paper with hot water, the usual procedure before titration. This extent is shown 1 2
S. B. Kuzirian, J. Am. Chem. Soc., 38 (19161, 1996. I n plant analysis Mn is a p t t o be occluded. The revised official
method recommends t h a t calcium be reprecipitated. Report of Committee on Editing Tentative a n d Official Methods of Analysis of t h e A. 0. A. C., 1915, 31. 8 J . B i d . Chem., 7 (1910), 8 3 ; 10 (1911), 87. After each set of filtrations i t 4 Ignited asbestos improves with use. is freed from acid and saved for further use.
