146 Drs Turner and Christison on the effects of 



ed with 10,000 parts of air, destroyed the whole vegetation of 

 a plant of considerable size in less than two days. Nay, we 

 afterwards found that a tenth part of a cubic inch in 20,000 

 'volumes of air had nearly the same effects. In twenty-four 

 hours the leaves of a laburnum were all curled in on the edges, 

 dry, and discoloured ; and though it was then removed into 

 the air, they gradually shrivelled and died. Like the sulphu- 

 rous acid, the hydrochloric acid gas acts thus injuriously in a 

 proportion which is not perceptible to the smell. Even a thou- 

 sandth part of hydrochloric acid gas is not distinctly percepti- 

 ble ; a ten thousandth made no impression on the nostrils what- 

 Qver, although great care was taken to dry thoroughly the 

 vessels used in making the mixtures. 



The other gases whose effects we have examined are chlorine, 

 nitrous acid gas, sulphuretted hydrogen, ammonia, cyanogen, 

 carbonic oxide, olefiant gas, and protoxide of azote. But our 

 examination of these has been cursory. 



Chlorine may be expected to have the effects of hydrochlo- 

 ric acid gas ; and so indeed it has ; but they appear to be de- 

 veloped more slowly. Two cubic inches in two hundred parts 

 of air did not begin to affect a mignonette plant for three 

 hours ; half a cubic inch in a thousand parts of air did not in- 

 jure another in twenty-four hours ; but when the plants did 

 become affected, the same drooping, bleaching, and desiccation 

 were observed. 



Nitrous acid gas is probably as deleterious as the sulphurous 

 and hydrochloric acid gases. In the proportion of a hundred 

 and eightieth it attacked the leaves of a mignonette plant in ten 

 minutes ; and half a cubic inch in 700 volumes of air caused a 

 yellowish green discoloration in an hour, and drooping and wi- 

 thering in the course of twenty-four hours. The leaves were 

 not acid on their surface. 



The effects oi Sulphuretted hydrogen are quite different from 

 those of the acid gases. The latter attacked the leaves at the 

 tips first, and gradually extended their operation towards the 

 leaf-stalks ; when in considerable proportion their effects began 

 in a few minutes, and if the quantity was not great the parts not 

 attacked generally survived if the plants were removed into the 



