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but dark brown. If four or five hours elapse before tbe solution is 

 poured into the water, the resin precipitated is found to be com- 

 pletely black. And if the digestion is continued for several days, or 

 until there is no longer any production of sulphureous gas, the tur- 

 pentine is converted into a black porous coal, which does not contain 

 any resin, although a substance hereafter noticed may frequently be 

 separated from it by digestion in alcohol. 



When common resin was treated in the same manner, about 43 

 per cent, of the coal was obtained, which, after exposure to a red 

 heat in a loosely- covered platina crucible, still amounted to more 

 than 30 per cent., and appeared to possess properties very similar to 

 those of some of the mineral coals. 



Mr. Hatchett having obtained, in the manner above described, 

 yellow resin, brown resin, black resin, and coal, from a quantity of 

 common turpentine, dissolved a portion of each of these, and also of 

 the turpentine, in nitric acid, and then reduced the solutions to dry- 

 ness. The residua, which varied in colour, from yellow to dark 

 brown, were dissolved in distilled water, and examined by solution 

 of isinglass and other re-agents. 



1 . The solution of the residuum of turpentine was of a pale straw 

 colour, and did not contain any tan. 



2. That of the yellow resin resembled the former in every respect. 



3. That of the brown resin was of a deeper yellow, but did not 

 afford a vestige of tan. 



4. That of the black resin, on the contrary, afforded a consider- 

 able portion of tan. 



5. That of the coal afforded tan in great abundance. 



Hence it appears, that these modifications of turpentine yield tan 

 only in proportion to the quantity of their original carbon, progres- 

 sively converted into coal. 



Other substances, particularly various kinds of wood, copal, am- 

 ber, and wax, when reduced into coal in the humid way, were in 

 like manner converted into tan by nitric acid. 



But tan may, Mr. Hatchett says, be artificially produced, without 

 the help of nitric acid ; for if any of the resins, or gum resins, after 

 long digestion with sulphuric acid, are digested with alcohol, a dark 

 brown solution is formed, which, by evaporation, yields a mass that 

 is soluble in water or in alcohol, and which copiously precipitates 

 gelatine, acetate of lead, and muriate of tin, but produces only a 

 slight effect on oxymuriate of iron. 



In the subsequent section of this paper, Mr. Hatchett mentions 

 some circumstances which induce him to think that a natural pro- 

 cess, similar to those above described, sometimes takes place in peat 

 moors, and that tan has been, and continues to be, formed during 

 the gradual carbonization and conversion of the vegetable matter 

 into peat. Supposing this opinion to be correct, it seems, he says, 

 at first difficult to conceive how the formation of tan is effected 

 during the growth of those vegetables from which it has hitherto 

 been obtained ; but after adverting to the experiments and observe- 



