450 DR LYON PLAYFAIR AND MR J. A. WANKLYN ON A MODE OF 
to 400 cubic centimeters. The bulbs 6 are very small, being mere dilatations of 
the narrow tube. They are to contain the liquid to be examined. ‘The bends a 

and a should be on the same level, and thin, so as to admit of fusion by the lamp. 
Altogether, the apparatus should not weigh more than 65 erm. The following 
mode is employed in making an experiment with the apparatus. 
After being cleaned and filled with the dry air of the balance-case, the bulb- 
apparatus is weighed, and then transferred to the bath, being grasped by a retort- 
holder, which takes hold of the neck connecting the large bulbsC and C. The end 
A is then jointed to a hydrogen-apparatus by means of a small caoutchouc tube ; 
the other extremity D, which projects out of the bath through an orifice in the 
side of that vessel, is likewise connected by means of a caoutchouc tube, with a 
long narrow glass tube pointing downwards, and designed to prevent diffusion. 
Dry hydrogen gas is then passed through the apparatus to repletion. Whilst this 
is going on, warm water is poured into the bath—the hole in its side through 
which the extremity D passes being stopped up with putty, which makes a very 
convenient water-tight stopping. The addition of water is continued, until the 
bends aa are totally submerged. When the apparatus is full of hydrogen, the 
connection at A is interrupted, and the liquid, of which a vapour-density deter- 
mination is made, introduced at A. 
On re-establishing the communication with the hydrogen-apparatus, a stream 
of dry hydrogen passes through the dilatation 6, and becoming more or less 
saturated with vapour, enters the great bulbs C and C. 
No more liquid is placed in 0 than is sufficient to fill that bulb half-full; the 
three supplementary dilatations near 0 acting as safety-bulbs, to avoid the effects of 
splashing. 
The temperature of the bath is raised very slowly, the water being constantly 
stirred, so as to ensure uniformity of temperature. When the temperature is 
three or four degrees below the point at which a vapour-density determination ie 
required, the current of hydrogen is nearly stopped. 

