Experiments on Indigo. 48 1 



in the receiver wa8 of a clear yellow, containing little or no nitrous acid, but yielding a 

 ftrong fmell of bitter almonds ; though it was moil likely that the nitrous acid fhould have 

 decompofed the pruflic, (which I then thought I had reafon to confidcr as exifting in 

 indigo) yet after adding pot-afh to it, I tried it with fulphate of iron, and obferved no ap- 

 pearances of blue by that teft. 



I could now conjedlure it to be nothing elfe than laurel-water, of which it had every 

 indication} I therefore tried it on a kitten, to which about two tea fpoonfuls were ad- 

 miniftered, at three different times ; after each dofej it was feized with convulfions, which 

 were perfedlly obvious both to the gentleman above alluded to, (who did me the favour to 

 affift at the experiment) and to myfelf ; it, however, furvived the trial, owing, no doubt, to 

 the dilution of the liquor, which was not above a third part of that obtained from twenty 

 grains of indigo ; and if the above fliould be proved true, by repeated experiments, it fhows, 

 that the products of organized bodies may be imitated by art, a principle that has been denied 

 by many celebrated philofophers. 



I will now conclude with fome general remarks on the effecSts of certain fubftances on 

 Indigo itfelf. 



My chemical friend, to whom I have been fo often obliged in the courfe of thefe ex- 

 periments, expofed indigo to the a£l:ion of oxigenated muriatic acid gas, which has the 

 effect of changing it to the green, in contradi£lion to the theory that fuppofes indigo to 

 derive its blue from oxigen, and its green from the lofs of it. The nitrous acid turns it 

 yellow, as has been often remarked^^ and which yellow I have obferved, when the acid has 

 been weakened, returns to the green and blue by expofure to light. He alfo burnt a quan- 

 tity of indigo in oxigenous gas, fctting fire to it by means of a lens and the folar rays ; the 

 refidue was a brownifti white fubftance, which afforded the fame folutions and ap. 

 pearances with the other refidues of the indigo. 



. .; I have all along found that bodies capable of affording oxigen, have made indigo pafs firft 

 from the blue to the green, and afterwards to the yellow, and in this laft inftance to the 

 white, when the bituminous matter was deftroyed by rapid combuftion. 



I have it in contemplation to repeat mod of Hauffeman and Bancroft's experiments, and 

 cxpe£t to be able to prove, that when indigo is revived from its folution in an alkali, an 

 acid is always prefent, or formed, which renders the alkali incapable of diffolving the 

 indigo, by combining with it. 



I will only beg leave to mention here one conclufion, drawn from Hauffeman's ex- 

 periments, which is clearly erroneous. 



He expofed a folution of indigo by alkali and orpiment in carbonic acid gas ; and got the 

 fame effe£t as in oxigenous, viz. the abforbtion of the gas and the revivification of the indigo : 

 if I have not miftaken Dr. Bancroft, he brings this as an argument in favour of indigo re^ 

 ceiving the blue colour by abforpiion of oxigen, which can only be fo, on the fuppofition 

 that that mixture can decompofe carbonic acid, though it does not appear that any other 

 matter has that power than phofphorus, and that only when a ftrong heat is applied. 



Whatever 



