\vith the Serum or ivatery Fart bf ibe Blood. 243 



atfurtheft the d.iy fcillowing, proviclxxl it be kept ia a cool 

 place (lidlcred from tlie contad of the air, efpecially during 

 the fiimmer, when it alters nuich tnore calily. 



In cafe of doubt, iiiipeilion of the fluid alone may fervc to 

 determine its qiuility ; for the figns of its fennentaii ui are 

 very evident. This obfer\;ation is applicable alfo to the co- 

 iourincr liquor, but in a leis degree. It. follosvs from this 

 circinnltance, that the vcfTels which have been ufcd ior Con- 

 taining, preparing, or apph ing paint made with ferutn ought 

 to be wajiied every day. The fecond precaution to be taken 

 is. that as the re-action of the ferum and lime increafes in the 

 courfe of time, as well as the denlUy of the mixture, in ordtr 

 that it mav be preicrved in the neceirary ftate <jf fluidity, or 

 to diminifh or increafe it according to the nature of the fub- 

 ftances to be painted and the number of (Irata to be applied, 

 another vefllel filled with ferum mull be provided, to give to 

 the colouring liquor the neceflary fluidityl It theiice tolrovvs 

 that the mixture mult be prepared as it is ufed. 



Having alfured mvfelf of the fuccefsful and confiant eftciSts 

 of this kind of painting, I tried to mix it with different co- 

 louring fubftances, to render the application of the invention 

 more general. 



The well known re-a<?.lion of animal fubftances and of lime 

 on the metallic oxides, and particularly on ihofe in which 

 oxygen is united to the metal with little force., made me fuf- 

 pciit an alteration of fome colours when mixed with this li- 

 quid ; an alteration naturally produced by the feparation of 

 a part of the oxyeen from the metallic oxides. On the other 

 hand, the analogy which coloured chalks have with calca- 

 reous earth induced mc to believe that their combination 

 would be attended with the happielt refult. The oxides of 

 lead, copi^er, and arfenic, indeed, \mdergo a fingular altera- 

 tion in their refpeftive colours, when tliey are tmiled with 

 ferum and calcareous earth : but this is not the cafe with co- 

 ball green ; which on that account appears to me to be very 

 proper for being ufed as a colouring matter in this new kind 

 of painting. 'I'hofe earths, however, called red, green, black, 

 or yellow, which are of an argillo-calcareout; nature, when 

 mixed with tbefe fubftances, mav furnifh ditlcrcnt agreeable 

 colours of a durability equal to the bhielfh colour produced 

 merely by the mixture ot lime and of i'erum. 



I have however remarked, that the durabllilv of this paint- 

 ing i* conliderably altered when thelcis mixed with it a verv 

 largt! qvuntiiy of cfilouring earth, fiich as ihe black earth ufdl 

 for p.iinlmi an iron colour, or the reprefentation of white 

 niiible vviih black fpots. To'rdmcdy this inconvenience, no- 

 li i thino; 



