1 16 Analysis of several Varieties of 



The following; table shows the quantity of water con- 

 tained in several kinds of salt, inferred from the loss which 

 they sustain by ignition during equal times, after being- 

 first dried at 212°. 



100 parts of large-grained fishery salt contain of 



water 3 



100 foreign bay salt (St. Martin's) .... 3 



100 ditto (Oleron) S| 



100 ^ . . . ditto, Cheshire common salt li 



100 ditto stoved salt o£ 



The loudness and violence of the decrepitation was, as 

 nearly as could be judged, in the same order, and was most 

 remarkable in the large-grained varieties. 



To determine the proportions of real muriate of soda in 

 those varieties of artificial salt which are nearly free from 

 earthy muriates, I employed also the process of decompo- 

 sition by nitrate of silver. The following are the quantities 

 of fused luiia cornea obtained from 1 00 grains of each of 

 three varieties dried, previously to solution, at the tem- 

 perature of 212° Fahrenheit. 



100 gr. pure transparent rock s'alt gave of luna 



cornea 24 2 



100 . . . .stoved salt, remarkably pure 239 



100 fishery salt. do 237* 



The proportion of ingredients in the several kinds of 

 muriate of soda (setting apart the impurities) appears, 

 therefore, to be nearly the same in all. And as the very 

 minute quantity of water discovered by analysis is not 

 constant in the several varieties, it may be inferred to be 

 rather an accidental than a necessary ingredient; for in the 

 latter case an invariable proportion might be expected, 

 .conformably to the important law, establishing an uni- 

 formity in the proportions of chemical compounds, which 

 has been explained bv Mr. Dal ion, and confirmed by Drs. 

 Thomson and Wollaston. 



What then, it may be inquired, is the cause of those 



* From 100 grains of pure artificial muriate of soda, previously heated 

 to redness, Dr. Marcet has since informed me that he obtained 24*16 grains 

 of fused luna cornea. The weight^of the precipitates thrown down in my 

 experiments by nitrate of silver are not, I am aware, exactly those which 

 might have been expected from the table of the comparative proportions 

 of water given in the text. Each experiment, however, was twice repeated 

 with every precaution 1 could adopt, and with the same results. That dif- 

 ferent kinds of salt give different proportions of luna cornea, is proved also 

 by comparing the experiment of Dr. Marcet with the results of Dr. Black 

 and Klaproth, both of whom found the fused muriate of silver from 100 

 parts of common salt to weigh 2?>5 grains. 



differences 



