478 Dr. R. A. Smith's Remarks on 



sulphuric acid, the greater portion of the substance is vola- 

 tihzed with decomposition, the vellow body ieing Ukewise 

 produced, while sulphate of ammonia is formed in the sul- 

 phuric acid. Also, when heated alone, selenaldine is decom- 

 posed, with disengagement of a gas of most offensive odour. 

 Selenaldine is a base like thialdine ; it is soluble in dilute 

 hydrochloric acid, and reprecipitated by ammonia as a cry- 

 stalline mass. The hydrochloric solution also immediately 

 decomposes with evolution of a most offensiv-e odour. Sele- 

 naldine is altered in a similar manner by boiling with water. 

 The yellow body, the formation of which seems to be always 

 attended with a liberation of aldehydite of ammonia, when 

 collected is orange-yellow, amorphous, soluble in alcohol and 

 aether, and fuses, when heated with water, to a reddish yellow 

 mass, which remains soft for a long time. When heated alone, 

 this body is charred with evolution of an oil containing sele- 

 nium and possessing a most offensive odour. 



We did not obtain a decisive result when trying to produce 

 a teUuraldine, the tellurium which we employed in the pre- 

 paration of the hydrotelluric acid accidentally containing so 

 large an amount of selenium, that merely selenaldine was de- 

 posited from the purple solution, containing, as it appeared, 

 only telluride of ammonium. We intend to repeat this ex- 

 periment with tellurium free from selenium. 



LXXV. Some Remarks on the Air and Water of Towns. 

 By Robert Angus Smith, Ph.D.* 



tTAVING given considerable attention to the inquiiy into 

 the causes affecting the health of towns, I was anxious 

 to find what the real evil in their polluted atmosphere con- 

 sisted of; the air has been frequently examined, but the dif- 

 ferences found do not sufficiently account for the differences 

 perceptible in breathing for the first time in entering a large 

 town from the countiy, or for the very great difference in 

 the colour and appearance of both when contrasted side by 

 side, by an individual outside a town, having both before his 

 eyes. The accumulation is great in this case, it is true, but 

 therefore so much the more fitted for showing us its true 

 character. 



I first examined the rain-water taken from a cistern ; a little 

 was boiled down and the solid residue was like fatty matter, 

 which burnt and gave the smell of a fat, leaving afterwards 

 a strong odour of nitrogenized organic matter. As this 

 amounted to nearly one per cent., I was disposed to con- 

 * Communicated by the Chemical Society; having been read January 4, 



