64 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
The new deci-hydrate * was obtained in quantity by concentrating ortho- 
phosphoric acid to 96 per cent, and keeping it at 24‘38°. Mechanical 
stirring for a few hours brought about crystallisation. The crystals are 
large, transparent prisms, similar in appearance to those of Joly’s hydrate 
and of anhydrous phosphoric acid. They were very hygroscopic, and 
were wiped dry and transferred to weighing tubes for the analysis in an 
atmosphere dried with phosphoric anhydride. 
Per cent, phosphoric acid found, 98T0 ; calc., 98T95. 
The specific electrical conductivity * of solutions of phosphoric acid in 
water was determined at concentrations ranging from 89’7 to 98 - 8 per cent. 
When the conductivity is plotted against the concentration, the curve is 
perfectly regular, and shows no points of flexure to indicate the presence 
of hydrates in solution. It will be recalled that, in the case of sulphuric 
acid, the corresponding curve shows a marked minimum at a concentration 
corresponding to the composition of the monohydrate, H 2 S0 4 H 2 0. 
The University of Chicago, 
August 1909 . 
* Journ. Am. Chem. Soc., 31, 1183 - 1194 . 
( Issued separately December 23 , 1909 .) 
