1 18 Analysis of several Varieties of Salt, 



the mean of which is 2033. Sir Isaac Newton states it at 

 2143, and Hasscnfratz at 2200*. All that was necessary 

 for my purpose was an approximation to the truth ; and 

 the introduction of a small error could be of no importance, 

 provided it were the same in every case, since the compari- 

 son would siill hold good. 



The specific gravity of rock salt, there can he little diffi- 

 culty in determining with precision. A piece of this salt f, 

 1 of such perfect transparency that I had reserved it as a 

 cabinet specimen, weighed in the air 513 grains, and lost, 

 when weighed in alcohol, 194 grains. The alcohol, at the 

 temperature of 56° Fahrenheit, had the specific gravity of 

 820, and hence that of the salt may be estimated at 2170. 

 Another specimen 'considerably less pure, and more ap- 

 proaching to a fibrous fracture, had the specific gravity of 

 2125 only. 



For ascertaining the specific weights of artificial varieties 

 of salts, T used a verv simple contrivance. It consisted of 

 a glass globe about 34- diameter,' having a stem or neck 10 

 inches long. Sixteen cubic inches of water (each 252| 

 grains at 60° Fahrenheit,) filled the whole of the globe, and 

 about half an inch of the lower part of the neck ; and from 

 the line where the water stood in the instrument, it was 

 accurately graduated upwards into hundredth narts of a 

 cubical inch. Into this vessel I poured exactly sixteen 

 cubic inches of a perfectly saturated solution of common 

 salt ; and then added 400 grains of the salt under examina- 

 tion, washing down the particles that adhered to the neck 

 by a portion of the liquid, which had been previously taken 

 out of the globe for the purpose. As much as possible of 

 the air which adhered to the salt was dislodged by agita- 

 tion, and the increase of bulk was then observed. 



Care was taken that the salts were all of equal temperature 

 and dryness, and thai no change of temperature happened 

 during the experiment. 



f 400 grains of the less pure kind of rock Hundredths *£*£* 

 salt, broken down into small frag- oi a - * n "grav.*ra»$ 



ments, filled the space of 75 2112 



400 grains of stoved salt 75 2112 



400 do. (another sample) 70 2084 



400 do. common salt 76 2084 



400 large-grained fishery salt 83 1 909 



400 do. (another sample) 83 1909 



400 St. Ube's . 82 1932 



* Anvalrs de Chimie, vol. xxviii. p. 13. 



f Foliated rock salt of Jameson. See his Mineralogy, vol. ii. p. 10. 



\ -Distilled water at 1000 being taken as the standard. If 



