144 Drs Turner and Christison on the effects of 



It is particularly worthy of notice that the proportion of 

 sulphurous acid which thus seems to be so deadly to plants, 

 is hardly or not at all discoverable by the smell. When a ten- 

 thousandth part of sulphurous acid gas was intimately mixed 

 with air, we could not be confident that its odour was percep- 

 tible, although we have reason to think our sense of smell is 

 acute ; and when this proportion was mixed in the same jar, 

 and in the same manner as in the experiments related above, 

 but without either plant or moisture being present, we were 

 certain that in eight hours no part of the air in the jar had 

 the slightest odour of the gas. This fact, though simple, is 

 an important one in regard to what has been stated in evi- 

 dence on some prosecutions against chemical manufactories,— 

 namely, that the emanations were not perceptible to the smell 

 in the neighbourhood of the works, and therefore not likely 

 to be in a state sufficiently concentrated to prove injurious. 



We do not pretend to infer, as an absolute conclusion from 

 these experiments, that manufactories from which sulphurous 

 acid gas is disengaged even in large quantities must be injuri- 

 ous to surrounding vegetation. It is probable, nay certain, 

 that, small as the proportion was which we have tried, the 

 proportion contained in the air in the vicinity of the largest 

 manufactories is a great deal less. But it seems certainly a 

 fair presumption, that, when such extraordinary effects are 

 produced in so short a time, by so minute a quantity, and 

 notwithstanding so liberal an admixture of air, effects analo- 

 gous, if not quite so fatal, will be produced by the lengthened 

 application of a larger quantity, though inferior proportion of 

 the same poison, in a state of constant renewal. 



The next gas, whose effects we have particularly examined, 

 is the Hydrochloric, or Muriatic acid gas. 



Its effects have appeared to us not inferior, nay even supe- 

 rior to those of the su]phar(}us acid. In our first experiments 

 with it we found that four cubic inches and a half mixed with 

 a hundred times their volume of air, and two cubic inches 

 mixed with four hundred volumes, began to turn the leaves of 

 a mignonette plant grayish-yellow in ten minutes, then caused 

 it to. droop, and in five hours killed it altogether and irreco- 

 verably ; and that the leaves were wet and acid. We next 



