An Eflajr on Bleaching* 2$J 



tnentation; on the other hand, this hemp may be employed 

 with great advantage in the arts. It is here proper to ob- 

 ferve, that bleaching by water never gives complete white - 

 nefs, like the ufual procefles of the bleach-field. To finifli 

 the bleaching of hemp, it would be neceflary to have recourfe 

 to the different means described in this eflay. 



Of Bleaching with the Oxygenated Muriatic Acid alone. 



In this procefs oxygenated muriatic acid is fubftituted for 

 the action of the air, and prefents itielf with advantage, be- 

 caufe its oxygenating principle is not drowned in a chaos of 

 different fluids, like the oxygen of the atmofphere ; its action, 

 too, muft therefore be fpeedier. As I have already examined 

 the principles of this acid, and its intimate nature, I (hall 

 now proceed to the application of it, and to a defeription.of 

 the bed apparatus. 



The matters which ferve for the production of the oxygen- 

 ated muriatic acid are manganefe, common fait, (muriate of 

 foda,) and the fulphuric acid, Mafiganefe is a metallic oxide 

 very much diffufed throughout the iurface of our globe, and 

 which may be procured at a fmall expenfe. The greater part 

 of it is brought to us from Macon, Saarbruck, and Hom- 

 bourg in the 1 ci-devant duchy of Deux-Ponts : it muft be 

 chofen well cryftallized in fmall black brilliant needles; and 

 it is neceflary to avoid with care thoie blackiih mafles, which 

 often contain heterogeneous matters, and, at any rate, the 

 matrix of this mineral. In order to employ it with advan- 

 tage, it mould be pounded before the mixture is made for 

 <diliillation. 



The fulphuric acid (oil of vitriol) ought to be concentrated; 

 that fold in the (hops generally (hows 60 Or 66 of the areo- 

 meter: it muft be taken as nearly as poffibl'e at that term, in 

 order to avoid errors in i\>< proportions of the fubftances ne- 

 ceflary for the diftillation of the oxygenated muriatic acid; 

 proportions founded on an uniform concentration. 



The fait to be employed ought to be white, and well cry- 

 ftallized ; it muft alfo be dried, and the cryftals, if lar^e, 

 muft be pounded, in order to facilitate the mixture with the 

 manganefe. 



The proportions generally obferved are, one part (by 

 weight) of manganefe j two of fulphuric acid, diluted with 

 a little more than its volume of water; and three of lalt. The 

 better thefe matters are combined together, the more eaiily 

 will the acid gas be difengaged by the action of the fulphuric 

 acid. It is proper alfo to remark, that the acid ought to be 

 diluted in a leaden vefiel; for, if other vefiels were employed, 



Vol. X. li they 



