36b ■ Decompojzti'm of the Acetite of Lead , 



It is therefore not fo much a new fa6t that I here prefent 

 as a development of one already known, which, as it forms 

 part of a general theory, dcferves to be particularly noticed 

 as one ot the cuiinus phasnomena in chemiftry. But to pro- 

 ceed in order, I think it neceffarv to refer to the work of that 

 celebrated cheiiiift already mentioned, where it is faid, in the 

 fixth feftion on metals, under the head Zinc, that 



^^ Zinc, bv its ftrong attra6tion for oxy2;en, decompofes 

 the greater number of falls and of metaUic lolutions; and that 

 it precipitates from them the metals under the metallic form 

 by completely unburnhio- them, or under that of oxides lefs 

 oxidated than they were before." 



This definition is no doubt juft, and feems to be perfeAly 

 complete. It is fufceptible, however, of the greateft deve- 

 lopment ; and particularly in regard to the difteient phaeno- 

 mena exhibited bv zinc in contati wiih aceti'.e of lead. It 

 is the union of thefc phsenomcna which forms the principal 

 fubjr'6l of the prefent obfervation, or rather the refult of the 

 ingenious experiment of Dr. <jlatk, which was communi- 

 cated to me a kw years ago, and to which I have made fome 

 additions. , 



Dr. Black put into aglafsjar, containing about four and a 

 half pints, twelve or fifteen decagrammes of cryftallized ace- 

 tite of lead. The jar was filled with water, and the mixture 

 being ftirred, it was left at reft for fifteen or twenty minutes, 

 or until the greater part of the fuperabundant fait, after the 

 faturation of the liquor, was fpontaneoufly precipitated. A 

 piece of zinc of an indeterminate weight was then fufpended 

 in the flightly turbid liquor by means of a hemp or filk 

 thread fixed to the cover of the jar, and the vcflel was depo- 

 fited in a place where it was not expofed to be (haken. At 

 the end of from twenty to twenty-five days decompofition 

 ■was completely effetSfed ; the zinc, fufpended in the middle of 

 the liquor, become diaphonous, was covered by a kind of very 

 briihant metallic vegetation, which was often continued to 

 the bottom of the veflel, and which Dr. Black called the 

 tree of Saturn. 



Having had occafion to repeat this experiment a great 

 number of times, it conduced me to feveral obfervations, in 

 confequence of which I refolved to make fome changes in it, 

 •which, as they do not alter in any manner the chemical na- 

 ture of the operation, contribute in a fingular manner to the 

 beauty of the refult. Thefe changes chiefly relate to the 

 hemp and filk threads, which, being eafily dedroyed by re- 

 maining in the liquor, muft neceflarily fuffer the zinc to fall, 

 and along with it the new metal which covers them. I 

 5 therefore 



