2 Thomson, Influence of Moistii7'e on Metabolism. 



investigate this subject on a larger scale than I had done 

 previously. I therefore constructed an a[)paratus consist- 

 ing of a lead tube, 3 inches diameter and 4^ feet long, 

 bent at right angles at both ends, flanged at each end, and 

 provided with lead-covered lids and rubber washers fixed 

 down by screws when the apparatus was not in use. 



This tube was filled with pumice stone and pure, 

 strong sulphuric acid, poured in to about one-fourth its 

 remaining capacity. An electric fan was connected with 

 one end of this tube, through which air was drawn and 

 delivered from the fan in a constant stream to give the 

 supply of dried air, the air being comfortably and naturally 

 inhaled from the stream and one exhalation, including the 

 residual air from the mouth and throat, delivered into a 

 small copper gas-holder, counterpoised by weights to 

 allow the air to be put in without strain upon the lungs. 



The air from the drying apparatus was unfortunately 

 not free from taste and smell, and it was then discovered 

 that the sulphuric acid had acted upon either the lead or 

 on impurities in the pumice stone and had produced 

 traces of sulphur dioxide. This was fatal to the experi- 

 ment, as it had been previously shewn by me that minute 

 traces of irritating substances, such as exist in the air of 

 towns, had the effect of largely reducing the percentage 

 of COo- in the exhaled air, as compared with the air of 

 the country where these are absent. 



I endeavoured to prevent the formation of this im- 

 purity by the addition to the sulphuric acid of a small 

 quantity of chromic acid, but this introduced another 

 unexpected impurity, viz., a trace of chlorine, and this 

 appliance was finally abandoiied in favour of a large 

 bottle filled with broken glass and wetted with strong 

 pure sulphuric acid. The warm air experiments were 

 made by adjusting a coiled length of manganin wire 



