DURABLE AND SUPERIOR LAKE. 215 



It appears that W. F. C. has not noticed thefe lines. The 

 production of nitric acid by fynthefis, being here clearly fiated, 

 his animadverfion relative to that fubject falls to the ground. 



To exculpate myfelf from his further accufation, namely, ofO^""? 1303 " 

 not having noticed the production of nitrate of potafh by arti- 

 ficial means, or rather having fiated it by implication, will be- 

 come equally erroneous, on reminding him, that the method 

 of preparing this fait artificially is pointed out, Vol. II. page 

 287, thus, " Nitrate of potafh may be prepared by neutralizing 

 carbonate of potafh xvitli nitric acid." 



From what has been fiated, it is obvious that W. F. C.'s 

 remarks are not correct, for both the methods of obtaining ni- 

 tric acid, and nitrate of potaih are correctly given, and not by 

 implication, as W. F. C. apprehends. 

 I have the honour to be, Sir, 

 Your's, 



FREDERICK ACCUM. 



XIII. 



Procfjfts for obtaining a durable and fapcrior Lake from Madder. 

 By Sir H. C. Englefield, M. P. F. R. S* 



1 HE want of a durable red colour, which fhould poffefs Introduction, 

 fbmething of the depth and tranfparency of the lakes made 

 from cochineal, firft induced me to try whether the madder 

 root, which is well known to furnifh a dye lefs fubject to change 

 by expofure to air, than any other vegetable colour, except 

 indigo, might not produce fomething of the colour I wanted. 



Several of the mofi eminent painters of this country have, Madder lakes 

 fcr fome time, been in the habit of ufing madder lakes in oiI re a a v d e "fedV^ut 

 pictures : but the colours they poffeffed under this name were they were bad. 

 either a yellowifh red, nearly of the hue of brick-duff, or a 

 pale pink opake, and without clearnefs or depth of tint, and 

 quite unfit to be ufed in water-coloured drawing, which was 

 the principal object of my fearch. 



My firft attempts were to repeat the procefs given by Mar- Margraf s pro- 

 graf, in the Memoirs of the Academy of Berlin : but the co- "J k a JJj^ 



* From the Trahfactions of the Society of Arts, who voted the 

 gold medal in honour of this difcovery. 1804. 



lour 



