Operation of ^qua Regia [Book VL 



detaches the muriatic acid, which rifes with the re- 

 mainder of the nitrous acid, and thus an aqua regia 

 is produced, jdly, By mixing a folution of alum 

 with nitre and common fait, in which cafe the vitriolic 

 acid of the alum difengages the nitrous and muriatic 

 acids by its fuperior attraction for their bails. 



It is ufual to make aqua regia by dilToJving fal 

 ammoniac in about four times its weight of ftrong 

 nitrous acid : but the refults of experiments or opera- 

 tions vary confiderably according to the proportion of 

 the ingredients made ufe of. 



The theory of the operation of this compound acid 

 does not feem difficult. In the courfe of this work it 

 has been more than once remarked, that the eafy fo- 

 lution of metallic matters in acids does not depend 

 merely on . the degree of attraction which exifts be- 

 tween the metal and the acid, but alfo on the eafe 

 with which the acid parts, with oxygen to calcine the 

 metal. From this caufe it happens, that the nitrous 

 acid, which has much lefs affinity with metallic matters 

 than the vitriolic or muriatic, (diffolves them more 

 readily than either of thefe. Aqua regia, however, 

 confifls of the acid which has the ftrongeft attraction 

 for metallic bodies, and alfo of that which moft eafily 

 parts with oxygen, and the union of thefe powers pro- 

 duces the effect of folution. That this is the true expla- 

 nation of the folution of gold in aqua regia appears 

 from fevefal circumftances ; for gold, previoufly re- 

 duced to the ftateofcalx, that is, furniihed already witli 

 a quantity of oxygen, is eafily diffolved by muriatic 

 acid, and gold in its metallic ftate,.is diflblved by the 

 oxygenated or aerated muriatic acid, and forms with 

 it the fame fait which is ufually obtained by the mixed 

 acid, or aqua regia. The muriatic acid, therefore, is 

 the true folvent of gold, and the addition of nitrous 



acid 



