Experiments in Voltaic Electricity. 421 



Metallic salts are also subject to similar changes. We see 

 then, that salts in general, alkaline, earthy, and metallic, partake 

 with barvtes of the property of being precipitated under similar 

 circumstances by their respective acids; — and generally, accord- 

 ing to the greater or less solubility of salts in water, they are 

 precipitated by their acids more or less concentrated. 



Had the facts here contained been generally known, the au- 

 thors of chemical rudiments must necessarily incur great censure, 

 for plunging deeper into mystery, that which is already intri- 

 cate : it must have involved many novices in the science into 

 the greatest difficulties ; for their first attempts are generally to 

 form the salts, and in performing which, if instead of solution 

 they obtain a precipitate, they conclude that the experiment by 

 some unknown accident has failed, — they refer to the instructions 

 and repeat the experiments in vain ; and this they are subject to, 

 not only in the formation of alkaline and earthy salts, for ma- 

 tallic salts, as we have seen, are included in the common error. 

 What can be a greater discouragement ? — But long after, when 

 least expected, thev bv some fortunate accident obtain by means 

 of a dilute acid the earnestly sought-for solution ; this event 

 steals on them, not as a discovery, for they charge it to their 

 own ignorance rather t'lan the instructor's neglect. Water then, 

 when required to the effect, should be expressed; as it cannot 

 be supposed that one who is ignorant of its properties can un- 

 derstand that it should in this case be present, when in many 

 experiments its absence to a certain degree is absolutely neces- 

 sary. 



Rudiments should be such, that the inexperienced learner 

 should obtain by them a competent knowledge of those laws 

 by which the more abstruse parts of a science should become 

 less difficult, as he has been more arduous in imbibhigthe means 

 of success. 



Under these circumstances, I camiot forbear to advise the 

 authors of chemical rudiments, to explain more clearly that it is 

 the acid which unites with the base, and the water alone which 

 dissolves this combination. 



Your obedient servant, 



Nov. 1.5, 18lo. H. 



LXXVIII. Experiments in. Voltaic Electricity. By Andrevv 

 CRossJi, Esq. In a Letter from the Author. 



To Mr. Tilloch. 



Sm, — aIaving seen a statement in your Magazine for August, 

 that M. Dobereiner of Jena subjected mercury in contact with 



D d 3 water 



