2'4S Comparative Gravity of theUuman Body and Sea-JValer. 



would remain untouched, on account of its being subject to the 

 influence of a super-salt, and not to an acid. 



I have always conceived compact and regular formed crystals, 

 far from containing any extraneous matter, do in that form exist 

 in the purest state : but this your correspondent contradicts, 

 when he observes, The excess of acid is free, and merely essen- 

 tial to solution. L^t him then break a large crystal of sulphate 

 of iron, &c. and apply his test for acid ; and if it answers, I hope 

 he will allow me to class it among the super-salts, and not. tell me 

 that this acid is also free. Most of the earthy and alkaline salts* 

 are neutral, and are capable of being separated from acidulated 

 water by crystallization. This, as may be seen a!)0ve, is not the 

 case with metallic salts: but many of" their properties agree so 

 far that I shall at some future period trouble vou with an ac- 

 count of them. 



According to G. S. I should have to apologize for troubling 

 you with a subject already treated of by so able a chemist as 

 Fourcroy. My aim was, to prove the state in which the acid cXt 

 ists in metallic salts. Fourcroy, as I have since found, observes 

 there is always an excess of acid in metallic solutions, and does 

 not conclude this to be essential to them. I therefore conceive 

 your correspondent has equally failed in his endeavour to de- 

 tract from the originality of my opinion, and in his attempt to 

 condemn my conclusions as fallacious and contradictory. 

 Your obedient servant, 

 Sept. 16, 1815. Y[. 



XLVI. Comparative Gravity of the Human Body and Sea-r 

 IVater. By Knight Spencer, Esq. 



To Mr. Tilloch, 



Sir, — X HE fact that the human body is, bulk for bulk, lighter 

 than sea-water has been long known, and may be easily proved 

 by any one who has confidence to throw himself upon his back 

 in the sea, and there lie at full length with arms extended, but 

 without the least motion. I do not, however, remember to have 

 seen it any where recorded, hoiv much the human body is lighter 

 than sea-Avater. 



With a view, therefore, to ascertain this point, I have lately 

 taken the opportunity of a gmopth sea to throw myself on the 

 surface with flint stone? in each hand, my arms extended, and \ 



* As my opinion has been called in question, T sliall not presu 

 term them 3uj)er-salti till the fact is delefiniucd. 



found 



