. 496 JACKSON: lead acetate, lead oxide, water 



known at lower temperatures. ^ The 2- and the 3-hydrates have 

 not been known before, I beheve. The temperature intervals 

 were 4°, below 152°; 10°, between 152° and 212°; and 20°, 

 above 212°. 



Thaumasite, CaS04.CaC03.CaSi0.3.15HoO (fig. 1, C). Four- 

 teen molecules of water are expelled much like the first 4 of 

 magnesium sulphate. The last one is much more firmly held. 

 The temperature intervals were 3°. 



PHYSICAL CHEMISTRY. —Equilibrium in the system: lead 

 acetate, lead oxide, water.- R. F. Jackson, Bm^eau of 

 Standards. Communicated by G. K. Burgess. 



In order to obtain a firm basis for investigating the clarifi- 

 cation of raw sugar, a study has been made of the basic acetates 

 of lead from the standpoint of the Phase Rule. The analysis 

 of the basic lead acetates was performed by measuring the volume 

 of standard acid neutralized by the basic lead and the volume of 

 reagent required for the total precipitation of lead. For pre- 

 cipitating lead either sulphuric acid or sodium oxalate was used 

 in excess. In the former case the excess was measured by pre- 

 cipitation with barium chloride, in the latter by titration with 

 potassium permanganate. 



The basic acetates were synthesized by the interaction of 

 neutral acetate and lead hydroxide. The reaction proceeded 

 very rapidly and produced some striking phenomena. In one 

 instance the reacting substances quickly formed a solution which 

 rapidly solidified to a relatively insoluble crystalline compound. 

 In another case the unmixed components had the appearance of 

 nearly dry solid material, but upon vigorous shaking formed a 

 mobile liquid. The explanation of this is in the formation of 

 a very soluble basic compound. The equilibria were established 

 by at least 48 hours' agitation at constant temperature. The 

 solid phases capable of existence are as follows: 



Neutral lead acetate PbCCoHgOo)" . 3 H2O consists of brilliant 

 monoclinic prisms. It is stable in equilibrium with solutions of 

 itself and its solubility increases very rapidly in solutions of 



1 See Foote and Scholps, loc. cit. 



2 Detailed paper to be published in the Bureau of Standards Bulletin. 



