616 EXPRRFMENT STATION BECOBD. [Vol. 37 



Comparative analytical data witli the molybdate method indicate the accuracy 

 of the procedure. 



Approximate results may be obtained at the time of adding the citric acid, 

 since the amount of acid required is proportionate to the amount of phosphate 

 present. A solution of citric acid standardized against a known sample Is 

 added to the solution containing the precipitates untU it just clears. Results 

 within from 0.5 to 1 per cent of those obtained by the regular procedure are 

 secuT&l. 



For the determination of Lime in a complete analysis of phosphate rock the 

 following procedure Is proposed : A 0.5-gm. sample is treated In the same manner 

 as in the phosphoric acid determination. The add is entirely boiled off and the 

 i-esidue dehydrated. Hydrocliloric add is again added and the material heated 

 to dryness. Fifteen cc of concentrated hydrochloric acid is finally added and 

 the material boiled, after which 50 cc. of boiling water is added and the mate- 

 rial filtered and washed. 



Since iron can not be separated from the filtrate by the addition of ammonia, 

 because of the precipitation of caldum phosphate, ammonia is added until the 

 precipitate begins to appear, and then hydrochloric acid, drop by drop, until the 

 filtrate is clear again. Two cc. of hydrochloric acid is added in excess, the liquid 

 heated to boiling, and 5 gm. of crystallized oxalic acid added, and, after solution. 

 40 cc. of boiling saturated solution of ammonium oxalate. After boiling for 30 

 minutes the precipitate is filtered. w;ished, iijuited, and weighed as CaO, or dis- 

 solved in sulphuric acid and titrated with standard permanganate. The pres- 

 ence of the free oxalic acid keeps the iron in solution. 



The use of fused quartz and alundum crucibles in place of platinum crucibles 

 in phosphate woa*k was found satlsfactor>'. 



Directions for preparing magnesium mixture and the wash solution are in- 

 cluded. 



Determination of carbonates in limestone and other materials, J. F. Barkeb 

 (New York State Sta. TecJi. Bui. 62 (1917), pp. 5-7. fig. i).— An apparatus 

 which depends on the principle of the hydrometer and its manipulation are 

 described. 



In tlie apparatus the carbon dioxid is liberated from the material by dilute 

 hydrochloric acid and the weight of the hydrometer decreased by the e.scaping 

 gas. The rise of the graduated tube above the water thus records the per- 

 centage of carbonates from which the carbon dioxid was liberated. The 

 method requires no weighing or computation of results, since the latter are 

 given by direct reading of the graduated scale. 



Comparative analytical data with the standard method Indicate the accuracy 

 of the proposed procedure. Some notes on details of manipulation, composition 

 of limestone, and application of the method are included. 



A rapid method for the determination of water-soluble arsenic in lead 

 arsenate, H. A. Scholz and P. J. Waldston (Jour. Indus, and Bngin. Cheni., 

 9 (1917), No. 7, pp. 6S2, 68S).—A procedure similar to that noted by Gray and 

 Christie (E. S, R., 36. p. 715) Is described, as follows: 



Five-tenths gm. of the dried and pulverized sample or 1 gm. of paste Is weighed 

 into a 250-cc. volumetric flask. Two hundred cc. of recently boiled distilled 

 water is added and the mixture vigorously boiled for 3 to 5 minutes, allowed 

 to stand 10 or 15 minutes, cooled, made to volume, and filtered through a dry 

 paper. Two hundred cc. of the clear filtrate Is measured into a 500-cc. Erlen- 

 meyer flask, a few crystals of potassium lodld and 7 cc. of concentrated sul- 

 phuric acid added, and the liquid then boiled down to about 50 cc. It is then 

 diluted with cold water, made alkaline to methyl orange with sodium hydrorid, 



