EADIATION OF HEAT BY GASEOUS MATTER. 
63 
the deflection produced by the dried air being less than a single degree. On this day, 
therefore, the action of the aqueous vapour of the air was at least thirty times that of 
the air itself. 
Almost every week-day during the last four months experiments similar to the above 
have been executed, and in no case have I observed a deviation from the result that the 
absorptive action of the aqueous vapour of the air is quite enormous in comparison with 
that of the air itself. Further on I t\u 11 give an array of figures illustrating this point. 
As I became more and more master of my apparatus, and more acquainted with the 
precautions necessary in delicate cases, the absorption of air and the elementary gases 
diminished more and more. I was induced to abandon the use of pumice-stone as well 
as of chloride of calcium, and to construct my drying apparatus in the following way. 
The internal portion of a massive block of pure glass was pounded to small fragments in a 
mortar ; these were boiled in pure nitric acid, and afterwards washed several times with 
distilled water so as to remove all trace of the acid. They were then dried, afterwards 
moistened with pure sulphuric acid, and introduced by means of a funnel into a U-tube. 
The funnel was necessary to preserve the neck of the tube from all contact with the acid, 
the least action of which upon the corks used to close the tube was sufficient to entirely 
\itiate the experiments. At the top of each arm of the U-tube a quantity of dry 
fragments of glass was placed, so that if any dust or particles from the cork or sealing- 
wax chanced to reach the interior they fell upon the dry glass. 
Similar precautions were taken with the caustic potash tube. Pure white marble was 
pounded to fragments and subjected to the action of a dilute acid, which removed the 
outer surface of the fragments. These were afterwards washed in distilled water and 
dried, then moistened until pure caustic potash, and introduced into the U-tube in the 
manner already described. It was sometimes necessary to perform this operation daily, 
and never on any occasion have I used tubes to dry a feeble gas which had been pre- 
viously used to dry a powerful one. 
In the present communication I shall have to touch upon many subjects which for 
want of time I have been unable to develope. The following is an example of these. 
Choosing a day of suitable temperature and moisture — a day on which the human breath 
shows no signs of precipitation — the action of the substances expired from the lungs 
may be most strictly determined by our apparatus. By breathing directly into the 
experimental tube, the action produced by the sum of the products of respiration might 
be accurately measured ; by breathing through the sulphuric acid tube, the moisture of 
the breath would be withdrawn, and the difierence between the action then observed 
and the former action would give that of the carbonic acid. In this way the products 
of respiration might be estimated singly, and the influence of various kinds of food and 
drink, or of physical exertion, on the respiration might be investigated in a manner 
hitherto unthought of. 
I have to record the following experiments only in connexion with this subject. 
Placing a suitable tube between my hps, I filled my lungs with air ; a stopcock wliich 
