16 PROCEEDINGS OP THE AMERICAN ACADEMY 



Preparation of Materials. 



Baric Bromide. — This substance was prepared in five distinct 

 ways, with the intention of determining whether the salt is capable 

 of being obtained in a perfectly typical state. 



In the first place pure baric carbonate was prepared from pure 

 baric nitrate. To make this latter substance the baric nitrate of 

 commerce ("purissimum "), containing traces of strontium, calci- 

 um, potassium, and sodium, was recrystallized seven times from 

 boiling water by cooling. Baric nitrate is the most convenient 

 starting point for the preparation of a typical barium salt, since its 

 solubility rapidly diminishes with the temperature, and is so much 

 less than that of the calcium and strontium salts. Even after the 

 second recrystallization the alcoholic fractionally precipitated ex- 

 tract of a large amount of the mother liquor, which had been 

 evaporated with excess of pure hydrochloric acid, showed no trace 

 of calcium or strontium bands in the spectroscope. The pure salt, 

 which had been recrystallized seven times, was dissolved in a large 

 platinum vessel in water which had been distilled in a platinum 

 retort, and was treated with an excess of pure ammonia water 

 which had also never come in contact with glass or porcelain. Into 

 this perfectly clear solution was led a current of pure carbon di- 

 oxide, prepared by the action of pure sulphuric acid on sodic 

 hydric carbonate. It was found impossible to free such carbonic 

 acid from a trace of sodium, shown by conducting the gas into a 

 lamp flame, as long as the sodic hydric carbonate was dry. After 

 this last substance had been submerged under two inches of water, 

 the gas evolved was easily obtained in a perfectly pure state by 

 passing it through a sufficient number of washing bottles contain- 

 ing at first a weak solution of sodic hydric carbonate and finally 

 pure water. 



The pure baric carbonate was washed with hot distilled water 

 until twenty five cubic centimetres of the wash water showed no 

 trace of ammonia upon the addition of ISTessler's reagent. The last 

 washing was with water which had been distilled in platinum. 

 The snow-white preparation was dried and gently ignited over a 

 spirit lamp in a platinum dish. 



From this baric carbonate three different preparations of baric 

 bromide were made, by dissolving it in two different samples of 

 hydrobromic acid and varying other conditions. The first sample 

 of acid was prepared from perfectly pure bromine. This had been 



