While the calculation of ionic entropies was the immediate purpose for which these heat capacity measurements were made, the data so obtained should, nevertheless, have considerable value from other points of view. The preseiit paper contains the heat capacity results together with calculations of tlie entro2ies of thy throe salts The ionic entropy calculatioris will be presented i i i another publication. Materials. - -The precipitation of barium fluoride from aqueous solution gives a very firic- powder which would s t ~ mquestionable as a thtrmody namic reference state. The sample employed iri the following measurements was prepared by melting ''c P." bariuni nitrate and potassium fluoride together in il platinum crucible, a i d thdii extracting the potassium nitrate diid ewew barium nitrate from the cooled mrlt with til ) t water. 'The extraction was continued until t h c h wash water gave no test for either potassium ioii or nitrate ion The product appeared t o I K definitely crystalliiie O I L examinatioii with 'I microscope. .1nalyiis by precipitatiwi of bariuiti sulfate from dilutc nitric acid sointioii gavr 99.7 * 0.5' of the theoretical barium content 'L'he authors wish ti) extend t h w t h a i i h to I h Oliver L. 1. W i c i ~ ~ - ifor i tlie greater part o f t h t s work in prepaniig this sampic The tertiary lead phosphate mas prepared froin lead acetate and Wa2HP04,both of "L r." grade Hot, dilute solutions i f the twi ialt.; \I ere slourl\mixed with vigclrous siirriiiK, s n d tlir. resultinq precipitate was washed thoroughly and theii drictl by heating for several days d t e$OoO. &rtrolytic analysis showed thc theoretical u n ~ i i i i i i t o f l e a l within 0 2Yc. The cesium perchlorate was prepared from samples of r." ccsium iiitratc ar.d iodochloridc by the addition of perchloric acid in dilute solution. Chemical tests iridicattd the absence of appreciable a ~ o i i i i t s( ~ fiiitratc i 'r icidochloridr, while the absence of other alkali metals was e i tablished by spectroscopic examination ?'he product was dried by prolonged heating at 1 40" I'hc lack v f aiiv riw nc-a-the ice p)iiit in the heat
