CLASSIFICATION OF CHEMICAL AGENTS. ^rt 



wish to avoid 'mutation. Pearl shell and ivory are however 

 too diear to bring them even into use as plates, and tlie same 

 objection in a less degree lies againtt box wood. Glass, l>y p. ^-^^ 

 Mr. Walker's method, decomposed by the Swedish acid may, glass. 

 we all know, be easily used as a substitute for both plates 

 and blocks; but it must tir&t be ground flat, and that ex- 

 pense puts an end to its utility. The soft turtle-shell might Other materi- 

 ]>erh;ips, when veneered on wood, be found to answer the * 

 purpose of printing— but this again will depend on its abun- 

 dance. Silver also can be delicately destroyed by quick 

 silver so as to make a block for printing, the form of the let- 

 ters being first traced in varnish or thick oil ; but this would 

 only do for ciphers, or siaail heads or tokens, for obvious 

 reasons. I have also thought, that, if we could write on a Writing in 

 block of stone or plate of glass with an iak so thick as to relief. 

 leavtf the 'Words in relief, we might, by pressing putty on it, 

 take a cast sufficiently durable to make many impressions ; 

 or thus cast it in plaster of Paris from the relievo on the 

 smooth block, but this would print the words white on a 

 black ground; perhaps as good or better than black on 

 white, as less dazzling. 



There are other ideas, but these are enough I trust to 

 rouse our thoughts on this important subject, and lest 1 tire 

 you sshkJ your readers, l conclude by assuring you, that al- 

 though I have not the honollr^ t'© be known to you, 1 am 

 always, • ■ :b-i'^t: >■; 



, i/U diiw *si)nf* Jqu xiiii> J"* Yours, &c. 

 .: .v.r.l nt ..,. A. .. ;r,..w^.{- ^ Q. CUMBERLAND. 



Bristol, Nov, 17, 1810. 



: ' 9f r WM^ w in'm- i 



:> »(b9llB3 o.e.»ct vu\ 



On the Ciussification of Chemical Agents, By Marshall 

 Hall, Esq, F, R, M. S, E, In a Letter from the Author, 



To Mr. NICHOLSON. 

 Sir, 



JLN your Joui^iilil for Nbveriib^i '^dU'f^tiVe^given insertion 

 to a small communication from nie, ** On the Combinations 



of 



