40 DR. R. ANGUS SMITH ON THE 



near the sea 0*043 — rather more than in Manchester. 

 This favours the idea of oxygen coming from vegetation^ or 

 rather of carbonic acid being absorbed to such extent as to 

 influence the experiments. I do not obtain quite the same. 



Dr. ErOscoe has put down for Manchester 0039Z per cent. 



„ „ the country 0*0402 „ 



„ „ Manchester district.. 0*0394 ,, 



That the amount should be less or even equal in Man- 

 chester is scarcely to be explain ed^ especially as, even in 

 Geneva, Saussure found more than in the country. Had 

 the country places been mountainous, the observations 

 would have been better understood. 



At the same time I made some experiments which gave 

 higher numbers, varying from 0*049 P^^ cent, to '15 per 

 cent. These, with the exclusion of four which are very 

 high, give an average of 0"0544. The four were taken 

 under circumstances which make me believe they are cor- 

 rect; some places are continually exposed to gusts from 

 chimneys, which must contain a high amount of acid. 



Lately I undertook a much larger number of experiments, 

 using Pettenkofer's method of analysis. The bottle used 

 is of a different shape from Pettenkofer^s, and the bellows 

 are different, but the method is essentially the same. The 

 bottle has a very wide mouth, so as to allow the hand to 

 enter ; and drying is performed by means of a pure linen 

 cloth which has been washed in acid and distilled water. 

 This saves a great deal of trouble ; and repeated analyses 

 have proved that neither from the hand nor the cloth does 

 any hindrance to accuracy arise. The bellows pump is one 

 that I have used for emptying the bottles of air for the per- 

 manganate test. The bottle and pump are figured in the 

 first paper. When the bottle is cleaned and dried, the 

 baryta is added, and the elastic cover is then put on. 



The following results were obtained after nearly 200 ex- 

 periments were made in Manchester and London : — 



