714 EXPEJtlMEKT STATION HECORD. 



the usujil aujilytic.'il staudpoiiit, lead Liydro^eu arseimle in mixtures with tlio 

 l)asie arsenate can be easily detei-iiiiiied by flip folknA-ius described method: 



"Take a convenient amount of the finely powdered sample (;} to 10 gm.), 

 depending upon the amount of the acid salt present, which has been dried at 

 1(X)°, and add 200 cc. of a 5 i)er cent solution of carbon dioxid-free ammonium 

 hydroxid. Allow to digest with occasional shaking for a few liours at room 

 temperature, when the reaction should be complete. The supernatant liquid is 

 then filtered bj' suction from the insoluble basic salt by using a Buchner 

 funnel prejiared with a pad made of two sheets of filter paper with a layer of 

 asbestos between. The upper paper slmuld be a hardened filter. The filter is 

 finally washed thoroughly with recently ))oiled distilled water luitil free from 

 soluble salts. The final washings may be tested with lead nitrate solution to 

 ascort.iin the completeness of the removal of the ammonium arsenate. The 

 filtrate should be perfectly clear. In case there is difficulty in obtaining a clear 

 solution it may be overcome by refiltering through a Gooch crucible having a 

 thin layer of carbon black on an asbestos pad. The final filtrate obtained is 

 made up to convenient volume and an aliquot taken for the determination of 

 arsenic. After free ammonium hydroxid is removed by boiling, the arsenic is 

 determined by the modified Gooch and Browning method. The amount of 

 arsenic in the total filtrate calculated as As-Os and then multiplied by the 

 factor 7.G034 gives the amount of lead hydrogen arsenate present in the original 

 mixture. 



" This method has been tried out on a number of mixtures of known compo- 

 sition and in each case has given good results." 



" The results show that the precipitates obtained from the i-eactions of lead 

 acetate and lead nitrate with disodium hydrogen arsenate under certain con- 

 ditions are mixtures of lead hydrogen arsenate and the basic lead arsenate." 



The estimation of sulphuric acid, sulphates, potassium., and calcium, L. 

 Ledoux (Abs. ill Bui. 8oc. Chini. Bely., 28 (1914), No. 2, pp. 51, 52; Cliem. Ztg., 

 38 {19J4), No. 54, p. 575).— To 200 cc. of solution 10 cc. of concentrated hydro- 

 chloric acid and 50 cc. of a 2 per cent barium ehlorid solution are added for the 

 precipitation of the sulphates. The mixture is then shaken for one hour in the 

 cold. Calcium is precipitated with ammonium oxalate, and the potas.sium is 

 obtained as potassium platinic ehlorid and reduced when Avarm with mag- 

 nesium. 



Studies upon a new method for the quantitative estimation of potassium, 

 F. Makshall iCheiU: Ztg., 38 {1914), ^'os. 55, pp. 585-587; 58, pp. 615, 616).— 

 Of the known methods for determining potassium quantitatively the platinic 

 ehlorid and perchloric acid methods are the most frequently iisetl. although both 

 methods, but more especially the first named, have objectionable features. 



In the method proposed an aliquot of the solution containing the alkalis only 

 as chlorids and representing about 0.05 gm. of potassium oxid is placed in a 

 beaker and evapoi'ated to dryness on the water bath. The residue is dissolved 

 in as little water as possible (2 to 3 drops is usually sufficient), and an excess? 

 (20 cc.) of a 2 per cent alcoholic solution of tartaric acid (one which has 

 stood for several days over solid potassium bitartrate and has been repeatedly 

 shaken and then filtered) is added. After the precipitation is complete, from 

 10 to 20 cc. of a bitartrate-containing alcohol (06 per cent) is added and boile<l 

 for 10 minutes on the water bath. The beaker is allowed to stand covered for 

 24 hours, shaking, however, at intervals, and then the contents are transferred 

 to a weighed Gooch crucible. The precipitate is washed w'ith potassium bitar- 

 trate-alcohol and finally with pure 96 per cent alcohol, dried at 80° C, and 

 weighed as potassium bitartrate. By dividing the weight o1itaine<l by 3.092 the 

 corresponding amount of potassium oxid is found. 



i^ee also previous notes (E. S. R., 32. pp. 60S, 609). 



