52 DR. R. ANGUS SMITH ON THE 



even to the senses in the case of many gases^ and we must 

 learn that the effect of poisons on health is not in propor- 

 tion to the effect on the sensations. 



Let us consider what is meant hy this 86 in a million. A 

 room twice the size of one not unusual, or two 30 feet 

 long, 24 wide_, and 15 high, will contain 21,600 cubic feet, 

 or 37,324,800 cubic inches. If we introduce 0'Oo86 per 

 cent., we bring 3209 cubic inches of carbonic acid into 

 the room, which will be considered a large amount if 

 put together in vessels : it is nearly 12 gallons. During 

 fogs there will be an addition of nearly five times the 

 amount = 60 gallons, or 405 in a million. If we go to a 

 very moderately close building, we add 1235 in a million, 

 or 14 times the first amount, or 168 gallons. If we go to a 

 room as close as a crowded theatre, take the number given 

 for one in London 0*320, we add 2831 in a million, or 377 

 gallons. And when we come to the state of air in mines, 

 we have various numbers, in a few instances rising to more 

 than 2 per cent. — nearly a million cubic inches, which would 

 be 578 cubic feet, out of the supposed room, which does 

 not differ far from this in which I now speak [the Meet- 

 ing-room of the Literary and Philosophical Society of 

 Manchester] . 



In order to read off the amount in a million, there ought 

 always to be four figures after the decimal point. 



