310 



On an error in Dr. Thomson's Mineralogy. 



[April 



The Hari Fansamis equivalent to the A/aAaransw, and is supposed 

 to be a version of the Mahabharat. The Fejaleng purdna is the history 

 of Fejahf the Jaina king of Kalyan, and the rise of the Jangam sect. 

 The purdnas of the first twenty-four TirVhanlars or deified saints, are 

 not procurable. 



VIII. — On an error in Dr. Thomson's Mineralogy. — By Captain J. 

 Campbell, Assistant Surveyor General. 



In mineral analysis magnesia is one of the most difficult earths to 

 precipitate. It has the peculiarity of forming a great many seluble 

 double salts, and even its carbonate is partially decomposed by cold 

 water, so that a portion is taken into solution. These double salts 

 appear not to have been examined with sufficient attention by che- 

 mists; Rose in his Manual of Analytical Chemistry remarks that, in 

 precipitating magnesia as a carbonate, carbonate of soda cannot with 

 equal good consequences be employed instead of carbonate of potash,— 

 carbonate of magnesia, according to Mosander, forms with carbonate of 

 soda a double salt, this salt is decomposed, neither by boiling the so- 

 lution, nor by evaporating it to dryness; while on the contrary the ana- 

 logous double salt, containing carbonate of potash and carbonate of 

 magnesia suffers decomposition thereby. The wash water also dissolves 

 much more of tbe double salt containing soda, than of the simple 

 carbonate of magnesia, yet, for all that, were carbonate of soda employ- 

 ed to separate magnesia, a great excess would be obtained in the ana- 

 lysis. Dr. Thomson says, "the employment of carbonate of soda, in- 

 " stead of carbonate of potash, has also a tendency to prevent the for- 

 •« mation of the double salt, for soda-carbonate of magnesia, does not 

 " form nearly so readily as potash-carbonate." The easiest, and rea- 

 diest mode of precipitating magnesia, is from the ammonio-muriatic 

 solution, by adding an excess of ammonia, and then adding phosphate 

 of soda, when an immediate precipitate of ammonio-phosphate of mag- 

 nesia is thrown down. This salt is almost insoluble in cold water, and 

 therefore this method is the best, and readiest in a rough quantitative 

 analysis, sach as is desirable in the present state of our knowledge of 

 our Indian minerals. But unfortunately we are precluded from using it, 

 because chemists have not yet decided on the composition of the preci- 

 pitate. Hose says that after being ignited, it contains 36.67 per cent 



