1908] PIERCE—RESPIRATION CALORIMETER 195 
Convinced of this, as well as thoroughly dissatisfied with the insu- 
lating appliances which I had or could make in the laboratory, I 
went to my friends in the chemical laboratory of this university, told 
them of my difficulty, and asked for suggestions. Professor YOUNG, 
professor of physical chemistry, suggested trying some Dewar flasks. 
I take this opportunity to acknowledge my indebtedness, and to 
express my gratitude to Mr. Younc, for his suggestion is one which 
will be appreciated by any physiologist who tries the apparatus for 
this purpose. 
Dewar glassware is made in several shapes—cylinders, cups, and 
flasks. The flasks are made either tubulated or with closed round 
bottoms. The Dewar apparatus is made also silvered or unsilvered. 
The principle is si mple—double-walled vessels with the air between the 
two walls exhausted. Thus there is a receptacle surrounded more or 
less completely by a vacuum. Across this vacuum radiation or ab- 
sorption will take place at a rate inversely proportioned to the per- 
fection of the vacuum. If the walls of the vessel are silvered on the 
surfaces bounding the vacuum, the efficiency of the insulation will 
be greatly increased. The apparatus was devised for liquid-air exper- 
tments and is named for the inventor, the famous chemist at the 
Royal Institution in London. This double-walled glassware has now 
Come into commerce and may be bought, under the name of “ thermal 
bottles,” in drug stores and of the dealers in automobilists’ and 
campers’ supplies. It is used for keeping food or drink warm or 
cold, as may be desired, for many hours. Thus soup, milk, coffee, 
ce-water, etc., can be maintained at the desired temperature for 
‘stonishing lengths of time. The commercial bottles are protected 
against breakage by cases of metal or basketry, but since these 
do not improve the insulation materially, they are unnecessary in the 
laborato » and the thinner-walled scientific apparatus is much 
cheaper, besides being obtainable in a greater variety of shapes. 
In the experiments which I am about to describe, I used silvered 
Dewar flasks of about 250°° capacity, which were supplied by EIMER 
and Awenp of New York for $2.40 each. If imported duty free, as they 
Would have been had I not been impatient to use them, they would 
have Cost decidedly less. There should be at least two such flasks, 
fot it is desirable to use always a lot of dead or other check material 
