344 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ent paper recites briefly a series of experiments giving much greater 

 definiteness to the point in question and making it available for the 

 verification of thermometers. 



Preparation op the Manganous Chloride. 



As material for preparation the purest manganous chloride and 

 nitrate of commerce were used. Several preparations made in different 

 ways assured certainty in the product. 



The manganous chloride was purified in the first place by crystalliza- 

 tion and centrifugal treatment. Through these processes it was passed 

 four times, after solution in ordinary distilled water, and twice after 

 solution in the purest water. Porcelain and platinum dishes were 

 used. This preparation was called la. Two more crystallizations gave 

 16, which was found to have essentially the same transition point. 

 Sample Ic was made from the two last mother liquors by further re- 

 crystallization. This also gave the same point. During these crystal- 

 lizations traces of iron were found to exist in the otherwise very pure 

 initial salt ; these traces disappeared in the very early stages of the 

 crystallization. This was proved by qualitative tests, which were care- 

 fully verified by suitable blank determinations. 



The purity of the salt, as indicated by the transition temperature, is 

 shown by the following table. Obviously the transition temperature 

 may be used as a guide concerning the freedom of the salt from every- 

 thing except isomorphous substances, especially for the present purpose. 

 The crude original substance had a transition temperature of 57.91°: 

 the first fraction, 58.03° : the second, 58.05° ; the fourth, 58.072° ; 

 the sixth, 58.089° ; the eighth, 58.090° ; and the ninth, 58.089°. 



For the preparation of the chloride from the nitrate of manganese, 

 this nitrate was recrystallized until wholly free from iron. It was 

 precipitated as carbonate by means of redistilled ammonium carbonate. 

 This substance was prepared by distillation with water in a platinum 

 condenser and collected in a platinum dish in which the manganous 

 carbonate was precipitated. The precipitate was boiled with many 

 portions of pure water until no more trace of nitric acid was found in 

 the wash water. It was then dissolved in concentrated pure hydro- 

 chloric acid and the chloride was three times recrystallized to eliminate 

 the traces of chlorine due to the excess of nitric acid, and also the 

 traces of hydrochloric acid. The salt gave the same transition tem- 

 perature as the previous sample, although it had been passed through 

 such different treatment. Therefore it seems reasonable to infer that 

 both samples were pure. 



