100 An Ejfij' on Bleaching. 



is not fuffieient ; the gas cannot introduce itfelf to a fuffieient 

 depth into the (luffs, and the fuperficies only is whitened. 

 By taking advantage of the intimate knowledge which we 

 have of the nature of this acid, we ha-ve difcovered a procefs 

 much Ampler, more ceconomical, and more agreeable to the 

 principles of feience. 



The fulphurous acid, or that acid generated by the im- 

 perfect combuftion of fulphur, differs from the fulphuric acid 

 (oil of vitriol) by its containing lefs of the acidifying prin- 

 ciple, and by being, as we may fay, the mean term between 

 fulphur and the fulphuric acid. As we are defirous that our 

 work ihould be underftood in manufactories, we fhall fpeak 

 only very briefly of the chemical properties of the fulphurous 

 acid, and (hall proceed to the method of preparing it. 



Sulphurous acid gas unites very eaflly with water, and in 

 this combination it may be employed for bleaching wool and 

 iilk. The fulphurous acid in this ftate of liquidity may be 

 prepared by making it traverfe water in an apparatus nearly 

 fimilar to that ufed for preparing oxygenated muriatic acid™ 

 The moft ceconomical method of obtaining it is, todecom- 

 pofe fulphuric acid (oil of vitriol) by the mixture of any 

 combuftible matter capable of taking from it a part of its 

 oxygen. In exa& experiments of the laboratory, where the 

 chemift is defirous of having great purity, it is obtained by 

 means of metallic fubftances, and particularly by mercury; 

 but for the purpofe of which we are treating, where great 

 ceconomy is required, we would recommend the moft conrr 

 mon fubftances. We fhall therefore give the following 

 procefs : 



Take chopped ftraw, or fawduft, and introduce it into a 

 matrafs; pour over it fulphuric acid, applying at the fame 

 time heat, and there will be difengaged fulphurous acid gas 

 (vapour of fulphur), which may be combined with water in 

 the following apparatus, and by the following method : 



Place long necked matrafTes on a furnace, and make them 

 communicate with a tubulated flafk into which a little water 

 has been put to abforb the fmall portion of fulphuric acid 

 (oil of vitriol) that may pafs without being decompofed 

 through this firft refervoir. Care muft be taken to apply 

 a fmall fafety-tube, one of the extremities of which muft be 

 immerfed fome lines in the water; to guard againft absorp- 

 tion. -A tube with a double bending conduces the acid into 

 flafks or other veifels, where it muft at length combine with 

 the water. 



We would propofe ufing, inftead of the tubulated flafk, 

 ft cylinder of lead, or of fir j or any white wood, hooped with 



■ • ; varnifhed 



