po Pnpji-tilkn of Adds for Blatching Ruw Sili. 



To p'lrify it, one humlred pounds of tliis vitriolic acid is to be mixed in a large bafon 

 of copper with the fame quantity of river water, and (lirred with a wooden fpatula. The 

 mixture inftantly becomes heated to the boiling-water point, and a great quantity of red 

 vapour is difengaped, which has the fmell of aqua-rcgia, and arifes from the nitrous and 

 marine acids. When this mixture is made, it is proper to immerfe the bafon to a fuitable 

 depth in a large velTel of water, to haften the cooling. As foon as it is fulficiently cooled 

 it is to be drawn off into bottles, and left to become clear during feveral days. Great 

 part of the fulphur falls down. The author obtained from four to fi.\ drams. 



A gallery mud be provided, on which two rows of iron pots of eleven or twelve inches 

 in diameter are to be properly placed for feparate fand-baths, as M. Baume always praaifed 

 in the fublimation of fal-ammoniac. By this means the retorts are ifolated, and if one 

 breaks, the acid cannot diffufe itfelf and break the others in its vicinity. An empty retort is 

 then to be placed in each pot, and covered with fand. In this way they are much more 

 convenient to arrange, and are attended with no rifle. 



The acid is in the next place to be decanted and conveyed into the retorts by a fyphon 

 funnel, and the reclification 'proceeded upon until it becomes perfcftly white. Towards 

 the end of the operation a fmall quantity of fulphur fublimes in tlie neck of the retort. 

 Inftead of receivers a fmall glafs cup is placed beneath the aperture of each retort, in order 

 to facilitate the diflipation of the nitrous and marine acids. 



When the acid in the retorts is fufficicntly cooled, it is poured a fccond time into tlic 

 copper bafon, and mixed with loo pounds of river water, as at firil, and again concen- 

 trated in the retorts till it becomes perfeflly clear. Sulphur has been afforded in fomc 

 inftances by the fecond redification. The liquor which diltills is received in the cups as 

 before, and the acid in the retorts is then fulficiently pure: that is to fay, it is purified from 

 all volatile matter. The lead and neutral f.dts ftill remain combined with the acid, 

 but fortunately they can in no refpeft. injure the purity of the marine acid 



This concentrated acid exhibits 68 degrees by the hydrometer, or fpecific gravity i.8:y(J. 

 It ftill contains a portion of gas, but fo fmall in quantity as not to injure the purity of the 

 marine acid, to which it only gives the property of cryftallifing when the temperature of 

 the air is near the freezing point. 



During the reftificition of this acid, what firft comes over is mere water, and muft be 

 thrown away; but tliat which fucceeds is the aqueous acid. If this be fet apart, and con- 

 centrated, a confiderable quantity of vitriolic acid is obtained of the greateft purity. As 

 it has been carried over in diftillation, it contains no foreign matter. 



The author attempted, but in vain, to diffipate the nitrous acid from the acid of vitriol 

 by ebullition in an open veffel without concentration. The experiment was made with 

 50 pounds of common vitriolic acid and 60 of river water. This was kept boiling in the 

 copper bafon for four days, water being added from time to time to fupply the lofs by eva- 

 poration. The copper bafon, by weighing before and after the operation, had loft by folution 

 no more than ten drams of copper. The acid was blue, but became white as ufual during 

 the reiflification in the retorts. From this experiment, as the author obferves, it is feen 

 not only that the nitrous acid cannot be difljpated by fimple ebullition without concen- 

 tration, but that the adtion of the vitriolic acid upon copper is extremely flight. 

 The marine acid is to be difengagcd from common fait by the application of this vitriolic 



acid 



