60 DR. R. ANGUS SMITH ON 



We see clearly how differently this substance acts from 

 carbonic acid. I took home a small piece of cotton-wool 

 over which the gas had passed for some days ; my intention 

 was to examine it with the microscope. Less than a grain 

 of this cotton was taken out of the tube in which it was 

 enclosed ; but so thoroughly did the room become offensive, 

 that some friends, not aware of my pursuits, were much 

 annoyed. 



This leads to the conclusion that the amount of car- 

 bonic acid is entirely incapable of showing the true con- 

 dition of an atmosphere, unless we estimate that gas at 

 once on its formation, as then it is mixed with organic 

 matter, if it is formed out of animal substances ; if, how- 

 ever, we allow even a short time to pass, a separation takes 

 place, the carbonic acid diffuses, and the organic matter 

 clings to surrounding substances. If the gas were pre- 

 viously passed through charcoal, it was difficult to obtain a 

 trace of organic matter. 



A trace of a compound of cyanogen was found, and a 

 small amount of phosphoric acid was obtained in the acid 

 solution. Ammonia was found in considerable quantities. 

 These substances exist along with the gases, and are all I 

 have hitherto determined. 



If carbonic acid were a measure of atmospheric impurity 

 of any real value, then the result would be that there are 

 no unwholesome atmospheres in nature ; but it is one so 

 gross and valueless, that it is only found in excess when it 

 is already known by loss of strength, or of life itself, that 

 the air is pernicious. 



In estimating the carbonic acid and the sulphuretted 

 hydrogen, we include the organic substances. A portion of 

 the latter, as has been seen, is taken up by the acid salts 

 of metals ; and when the residue is passed over soda, the 

 smell is entirely removed and gases remain. These organic 

 substances seem to be the truly injurious portions of the 



