10 Historical Sketch of Improvements in [July, 



merely to give up the use of oxygen as a cure for consumption, 

 but to adopt a gas of a very opposite kind. Carburetted hydro- 

 gen gas dihited with a certain proportion of common air was 

 inhaled by consumptive patients with apparent good effects. 

 The late Mr. Watt, who had interested himself very much in. 

 these investigations, and who possessed much more sagacity 

 and acuteness than any of his coadjutors in the promotion of 

 pneumatic medicine, as it was called, retained his belief of the 

 good effects of this last remedy in consumptions to the very 

 last. The very last time that I was in his company (about a 

 year before his death), he happened to broach the subject, and 

 he expressed himself with considerable confidence. The readers 

 of the Annals of F/iilosuplii/, to many of whom these facts must 

 be familiar, would, therefore, see with surprize that a mixture of 

 oxygen and azotic gases from saltpetre had been used in the 

 United States with success as a cure for consumption. — (See 

 Annals of Philosophy, xiv. 71.) 



2. Chlorine. — It has been ascertained that chlorine has the 

 property of combining with lime, barytes, strontian, potash, 

 soda, and several other bases, and of forming with them chlo- 

 rides, which possess the property of whitening vegetable bodies. 

 One of these, the chloride of lime, has been long used to a very 

 great amount in Great Britain and Ireland, to bleach cotton and 

 linen cloth. It is known by the name of bleaching poicdcr. 

 Besides the manufactories of this powder in Great Britain, there 

 are no fewer than four in Ireland. This powder varies consider- 

 ably in its goodness, according to the care with which it is 

 manufactured, and the length of time that it is kept, and hitherto 

 no verv"- unexceptionable mode of analyzing it had been sug- 

 gested by chemists. I have some considerable hopes that this 

 defect has been in a great measure supplied by the method of 

 analysis which I inserted in the last number of the loth volume 

 of the Annals of Philosophy. I have repeated it several times, 

 and found the results to agree so well with each other, and to 

 correspond so well with the discolouring powers of the powder, 

 that 1 consider it as entitled to confidence. The process is 

 attended with as few difficulties as any other mode of analyzing 

 so complicated a substance with which I am acquainted. Bleach- 

 ing powder always contains the following substances : 



1. Subbichloride of lime, 



2. Muriate of lime, 



3. Unconibined lime, 



4. Water. 



Of these, the only substance of any importance to the 

 bleacher is the first. Now its weight may be determined by the 

 first step of the analytical process, as follows : 



Put 1000 grs. of the bleaching powder into a retort, the beak 

 of which, by means of a long tube luted to it, is connected with a 



