870 



SCIENCE 



[N. S. Vol. XXXm. No. 857 



stant stream of pure water could be run 

 through the sample and collected for evapora- 

 tion to a suitable volume vcould likely be the 

 best method for determining relative water 

 solubility. 



Lahoratory Preparation of Lead Ortho- 

 arsenate. — Very few American chemists appear 

 to have experimented with the ortho-arsenate 

 of lead. Probably this is due to the fact that 

 the formulas most often published do not 

 produce this compound in the pure state, that 

 is : unmixed with acid arsenates. True ortho- 

 arsenate may be prepared as follows: 



Solutions of lead acetate or nitrate and 

 arsenic acid or ammonium, sodium or potas- 

 sium arsenate containing the correct weights 

 of the oxides (1 part of As.O^ to 2.90 PbO) 

 are poured together. The water should be 

 suiEcient to dilute the precipitate so that it 

 will not form too thick a mass. To this mix- 

 ture ammonia is added to strong alkalinity. 

 The mixture is digested with gentle heat for 

 an hour or more, allowed to settle, and the 

 clear liquid tested for arsenic oxide as de- 

 scribed under the ammonia test. If a precipi- 

 tate forms, a little more lead solution is added 

 and the procedure repeated until no precipi- 

 tate appears. It is well to wash the finished 

 product and again treat with ammonia. If 

 any arsenic oxide appears in the filtrate more 

 lead solution should be added. Finally wash 

 to the complete removal of water-soluble salts. 

 In accordance with well-known principles of 

 chemistry the retention of the arsenic oxide 

 wiU not be complete until there is an excess of 

 the precipitant, that is, lead oxide. For this 

 reason true ortho samples will show less than 

 the theoretical percentage of arsenic oxide 

 (25.59 per cent). With commercial samples, 

 where allowance has to be made for impurities, 

 this percentage is still further reduced. 



It appears, then, that the federal insecticide 

 and fungicide law rules out commercial ortho- 

 arsenate of lead prepared on a 50-per-cent. 

 water basis, by requiring 12.5 per cent, arsenic 

 oxide. The manufacturers may still comply 

 with the law by reducing the water percent- 

 age, but this is done at expense of easy remix- 

 ing, so working a hardship on the consumer. 



It is my opinion that this clause in the act 

 should be amended to read : " In the case of 

 strictly ortho-arsenate of lead, the arsenic 

 oxide content shall not be less than 11 per 

 cent, or more than 12.5 per cent, on a 50-per- 

 cent, water basis." 



Further Discussion of Water. — Haywood, as 

 already cited, has shown that chlorides, car- 

 bonates and sulphates may seriously increase 

 arsenical injury from acid and pyro-ortho 

 mixtures even when present in comparatively 

 small amounts. Some recent results with 

 these arsenates in commercial spraying ap- 

 parently bear out such conclusions. The 

 commercial ortho-arsenate usually contains 

 enough excess lead oxide to offset these eifects, 

 but eases can be imagined where this com- 

 pound might be partly decomposed. In sueli 

 instances it is clearly possible to overcome 

 the difficulty by treating the water with lead 

 acetate. The addition of lead acetate until 

 the water shows a reaction for soluble lead 

 should give the desired result. The presence 

 of small amounts of lead acetate will not 

 prove injurious, and we have applied the car- 

 bonate and sulphate in very large quantities 

 without producing the slightest injury. Lead 

 acetate will completely overcome the effects of 

 carbonates and sulphates and should greatly 

 reduce the solvent action of chlorides. 



Achnowledgments. — The investigations of 

 which the features of this discussion form a 

 part have had a wide scope and important 

 contributions have been made by several 

 people, among whom may be mentioned Pro- 

 fessors C. W. Woodworth, W. T. Clarke, Geo. 

 E. Colby and Mr. E. E. Luther. 



W. H. VOLOK 



WATSONVttLE, CAL. 



SOCIETIES AND ACADEMIES 



THE WASHINGTON ACADEMY OP SCIENCES 



The Washington Academy of Sciences held its 

 71st meeting in the auditorium of the New Na- 

 tional Museum on the evening of April 18, 1911. 

 President F. W. Clarke presided. 



Sir John Murray, of Scotland, gave a most in- 

 teresting and beautifully illustrated lecture on 

 "The Ocean." 



