No. 50.] 93 



contains scarcely any. In those made from sea-water by solar heat, 

 sand and fragments of shells and corals are generally found, some- 

 times to an amount equal to one-half of one per cent : they are 

 sometimes discolored, and a peculiar putrid odor is almost always 

 to be observed in them. 



The size, hardness, and density of the crystals of salt vary with 

 circumstances connected with the manufacture, and appear to have 

 no relation to the impurities which they may contain ; and the 

 same remark is true of the properties which are popularly attri- 

 buted to different kinds of salt : they must be owing to the size 

 and density of the grains, and not to the presence or absence of 

 impurities ; for an inspection of the above tables of analyses shows 

 that some of the purest, and others the most impure, are equally 

 reputable. This point has been maintained by others, and it is to 

 be hoped that the specimens and facts here presented may aid in 

 doing away the prejudices which are so common upon this subject. 



The method of analysis pursued is nearly that of the late Dr. 

 William Henry, as given in the Transactions of the Royal Society 

 of London for the year 1809. In separating the earthy chlorides by 

 alcohol, there is some uncertainty when sulphate of magnesia is 

 present. There is room for a great deal of variation in the results 

 of the analysis of common salt, from the impurities being so small 

 in amount compared with the whole, as well as from the fact that 

 specimens made in the same brine do vary in the amount of their 

 impurities. In computing the several compounds in the salt from 

 the bases and acids found, there is also some room for a difference 

 of opinion, but I have done it to the best of my judgment. 



My thanks are due to the gentlemen whose names are mentioned 

 in the list of donors, and to Mr. G. Washington Taylor, who has 

 aided me in verifying nearly all the results of my laboratory in- 

 vestigations. 



aEORGE H. COOK. 

 KuTGEEs College, Ne-w-Brunswick, N.J. 

 December 15, 1853. 



