359 



gravities, by putting equal weights successively into the same vessel, 

 and again weighing it after filling the interstices with a saturated so- 

 lution of salt. 



The specific gravity of rock salt was found, thus, to be. . 2125 



That of the same broken into small fragments 2112 



That of stoved salt was also 2112 



Common salt 2084 



Fishery salt 1909 



St. Ubes, as a specimen of bay-salt 1932 



The difference between the large-grained fishery salt and the bay- 

 salt of foreign manufacture is so inconsiderable, that although the 

 superiority of the former in chemical purity may not be considered 

 as of any advantage for economical purposes, yet in its mechanical 

 qualities it cannot be said to be inferior in a degree that can be pre- 

 judicial. 



The methods of analysis employed by the author in this inquiry 

 are next described. The salt to be examined was first dried at a 

 given temperature of 180. The earthy muriates were then sepa- 

 rated by alcohol, and their aggregate weight ascertained after evapo- 

 ration of the alcohol. An aliquot part was next dissolved, and the 

 lime precipitated first by carbonate of ammonia, after which the mag- 

 nesia was separated by phosphate of soda, as a triple ammoniacal 

 phosphate of magnesia. A previous trial having shown that 100 

 grains of dry muriate of magnesia would give 151 of the triple 

 phosphate, the quantity of muriate of magnesia was inferred from 

 this latter precipitate, and the difference between that and the ag- 

 gregate weight of the two muriates was considered as muriate of 

 lime. Sometimes the estimation was formed in a different way, by 

 superoxalate of potash, which was found to occasion a precipitate of 

 116 grains from 100 dry muriate of lime ; and thence, as before, the 

 weights of each might be inferred. 



For estimating the earthy sulphates, the quantity of original salt 

 that remained after affusion of alcohol was dissolved by long boiling 

 in water ; the earths were precipitated as carbonates by carbonate of 

 soda. The sulphuric acid was separated by muriate of barytes, and 

 thence estimated. The earths were then re-dissolved in sulphuric 

 acid, dried, and their weight ascertained. Of these sulphates, the 

 more soluble part was dissolved in a small quantity of warm water, 

 and the magnesia precipitated, as in the former case, as a triple 

 phosphate of magnesia. 



It was found that 100 grains of this precipitate indicate 111 of 

 crystallized sulphate of magnesia ; and hence the respective quan- 

 tities of the two sulphates was known : but since it was possible 

 that some proportion of alkaline sulphates might be also present, 

 some collateral experiments were necessary for the purpose of ascer- 

 taining whether the sulphuric acid obtained above by muriate of ba- 

 rytes, corresponded with that which would be contained in the mere 

 quantities of sulphate of magnesia and sulphate of lime discovered 



