46i Isochronous Clocks, 



phate of mercury.'* Now to wash soluble crystals in small quan- 

 tities of. water for the purpose of freeing them from any ex- 

 traneous matter, is in the operations of chemistry the most im- 

 perfect ; for a salt, without entire solution, cannot be subject to 

 the influence of water on all its parts; and as the washings are 

 acid from the commencement of the operation till after the yel- 

 low precipitate is formed, a neutral salt cannot be produced iu 

 any part of the process, but the whole of the mercurial salt is 

 carried off iu the state of a super-sulphate. If without the aid 

 of water we cannot discover the existence of acids (which is ob- 

 vious in those which are crystallized), any dry substance being 

 treated with water, and answering the acid tests, cannot in the 

 dry state be considered neutral ; as the properties of acids de- 

 pend so much on their combination with water ; and as when 

 water is added to the above-mentioned salt (the supposed sul- 

 phate) it is acid, it must in the dry state be an acid salt with an 

 excess of oxide mixed with it, caused by the evaporation of part 

 ©f the acid in the process of drying. I therefore conclude, in 

 the opinion tliat metallic salts cannot exist in the neutral state ; 

 for as iu the humid v/ay we discover acid properties in tliis class 

 «f salts, and as acids in the dry state do not possess acid proper- 

 ties, we must allow the metallic in every state to be super salts. 



Your obedient servant, 

 Ixindon, June 15, 1815. ff^ 



P.S. — This humble attempt, sir, is founded merely on the 

 success I had with those salts which I at the time happened to 

 be in possession of. 



LXXXI. On Isochronous Time- Keepers. By Mr. Thomas 

 Reid. 



To Mr. Tillock. 



Sir, — In your Philosophical Magazine for May last, a gentle- 

 man long eminent and respectable as a philosopher in the arts 

 and sciences *' has presumed" that .the two clocks of mine, 

 vhose rates of going were inserted in your Magazine of last 

 March, "might have been in the same circumstances'" as those 

 which he has mentioned. These kind of circumstances are not 

 new to me; such or similar observations of two clocks going 

 on in this ivaxj, and whose pendulums affected each other, were 

 nmde long ago by the late ingenious Mr. John EUicott, and may 

 have been made by otiiers besides him, for aught that I know. 

 But these clocks were not properly fixed, being on such elastic 

 leards as those v.hith Mr. De Luc mentions. I should have 



thought 



