270 DR. R. ANGUS SMITH ON THE 



and near habitations is the direct decomposition of organic 

 matter on the spot. If so^ being more readily observed 

 than organic matter itself, it may be taken as a test, and 

 the amoimt will be a measure of the impurity. A room 

 that has a smell indicating recent residence "will, in a 

 certain time, have its objects covered with organic matter; 

 and this will be indicated by ammonia on the surface 

 of objects. After some preliminary trials, seeing this 

 remarkable constancy of comparative results and the 

 beautiful gradations of amount, it occurred to me that the 

 same substance must be found on all objects around us, 

 whether in a town or not. I therefore went a mile from 

 the outskirts of Manchester and examined the objects on 

 the way. Stones that not twenty hours before had 

 been washed by rain, showed ammonia. It is true that 

 the rain of Manchester contains it also ; but, considering 

 that only a thin layer would be evaporated from these 

 stones, it was remarkable that they indicated the existence 

 of any. The surface of wood was examined; palings, 

 railings, branches of trees, grass (not very green at the 

 time), all showed ammonia in no very small quantities. It 

 seemed as if the whole visible surface around had ammonia. 

 I went into the houses and examined the surfaces in 

 rooms empty and inhabited, tables, chairs, walls, plates, 

 glasses, and drawing-room ornaments. A (Parian) porce- 

 lain statuette under a glass showed some ammonia ; a 

 candlestick of the same material (but uncovered) showed 

 much more. The back of a chair showed ammonia; when 

 rubbed with a common duster, there was very little. It 

 seemed clear that ammonia stuck to every thing. 



If, then, ammonia was everywhere, the conclusion 

 seemed to be that it was not at all necessary to do as I had 

 been doing — namely, wash the air so laboriously ; it would 

 be quite sufficient to suspend a piece of glass and allow 



