RICHARDS AND WELLS. — TRANSITION TEMPERATURE. 435 



The second sample of sodic sulphate was made by neutralizing with 

 sulphuric acid a quantity of sodic bicarbonate, which had been well 

 washed with cold water. The product thus obtained was recrystallized 

 many times, and readings taken as recorded below. 



Sam[)le III was later made from the filtrates of the various recrystal- 

 lizations, and sample IV was made from a mixture of I and II when 

 they became too small in amount to recrystallize separately. 



It was convenient in this preliminary work to take successive read- 

 ings of the transition temperature of several samples of salt, and then to 

 take the reading of the thermometer in melting ice. In all cases except 

 the first two, the lower fixed point was determined immediately after 

 the upper one. Since commercial ice was found to contain impurity 

 enough to change its melting point by several thousandths of a degree, 

 pure ice was made for the zero observations. The purest water, twice 

 redistilled, was frozen in platinum. After using some ice thus prepared 

 it was found that 100 grams of the resulting water gave, on evaporation, 

 a residue of only 0.0006 gram, the effect of which on the freezing point 

 would be negligible in this work even if it had all consisted of sodic 

 chloride. 



The results of these measurements, recorded in terms of the hydrogen 

 scale, were as follows : 



In the previous communication already quoted, this same thermometer 

 is reported to have given as the transition of sodic sulphate tlie value 

 32.482 in mercurial degrees, or 32''. 378 on the hydrogen basis. Tliiis it 



