RICHARDS AND PARKER. ATOMIC WEIGHT OP MAGNESIUM. 61 



The solution of ammouic chloride thus prepared was added to the 

 solution of magnesic chloride obtained by dissolving the oxyciiloride in hy- 

 drochloric acitl in proportions corresponding to formula Mg.Cl.,(NIl4)CI, 

 and the mixture was carefully evaporated to dryness and gently heated 

 in an oven. It is of course unnecessary to say that all the latter part 

 of this purification was done as far as possible in platinum. The solid 

 cake was powdered in an agate mortar, and placed in a glass stop- 

 pered bottle which was kept in a closed jar. The doable chloride 

 thus prepared was then tested with the spectroscope, but no impurities 

 could be discovered ; and its solution in water was perfectly clear. Tests 

 were made with amnionic oxalate and baric chloride, but in neither case 

 was a precipitate formed on long standing. 



The second sample of magnesic chloride was treated in a similar way 

 up to the point where it was necessary to get rid of sodium and potas- 

 sium. The solution was evaporated to dryness in a platinum dish with 

 the aid of an alcohol lamp, and the resulting cake was gently ignited and 

 then washed for a long time, nothing but platinum being allowed to 

 come in contact with the material from this time forth, and all the heat- 

 ing being done by means of alcohol lamps to avoid the danger of con- 

 tamination of sulphur from illuminating gas. The oxychloride thus 

 formed was then dissolved in pure hydrochloric acid and filtered. By 

 evaporating down again the magnesium was again rendered insoluble. 

 This process was repeated again and again, until there was no trace of 

 sodium or potassium remaining. 



The ammonic chloride necessary for the preparation of the double salt 

 from this second sample of magnesic chloride was prepared by digesting 

 ammonic chloride with nitric acid to destroy the amines.* It was then 

 dried, sublimed several times, recrystallized five or six times from its 

 aqueous solution, and again sublimed in a current of air which had been 

 passed through wash bottles containing respectively a concentrated 

 solution of potash and sulphuric acid. After having been sublimed in 

 this manner about ten or twelve times, it was dissolved in redistilled 

 water and added to the sample of magnesic chloride. The whole was 

 then filtered, evaporated to dryness, partly dehydrated, broken up and 

 placed in a glass stoppered bottle. The usual tests were made as to its 

 purity, but no traces of foreign matter were discovered. 



The third sample of magnesic chloride, which was used for the final 

 experiment in the last series, was at first treated in about the same way 



* Kruss, Liebig's Annal., CCXXXVIII. 51. 



