130 Mr. Walker’s Experiments on 
of -§ of an inch, by a thin partition c c* of one piece likewise 
with the vessel. 
D, is the cover or lid of this vessel, fitting over it water- 
tight,^ forming a bottom to the vessel, and having a rim ~ of 
an inch deep, as a stand to insulate it from the table ; the 
whole apparatus appearing to form, when together, one cylin- 
drical vessel, 8 inches high, and 4 inches wide.J The vessels 
A and B contain each 1 pint and ^ ; and the. tube a , and 
cup b , 1 ounce and \ each. 
N. B. The drawing, with the scale annexed, gives the sec- 
tion of this apparatus, of exactly the dimensions mentioned. 
The instrument described in Phil. Trans, for 1795, page 288, to 
• Having ascertained by experiment, that a stratum of air of this thickness did not 
prevent (during the length of time which is required to freeze the water, and reduce 
the ice to powder in the tube a) the materialsin the cup b from receiving the tempe- 
rature required, yet was nevertheless sufficient to impede the action of the mixture 
on the materials, when mixed in the cup b, during the short time required to take 
its temperature, or to freeze. the quicksilver, I adopted this method, in preference to 
letting out the frigorific mixture from the vessel B, immediately before mixing the 
last materials, as formerly. 
+ If this cover does not fit water-tight, it may be made so, by the intervention of 
a thin bladder previously soaked in warm water. 
$ For the purpose of ascertaining the proper proportion of the materials to be 
mixed at different temperatures, and other preparatory matters, I used an apparatus of 
the same construction as Fig. 3, Tab. XXIII. Phil. Trans, for 1795, but differing in 
having two tubes instead of one. The dimensions of this apparatus, being adapted 
to the same scale as the former, are thus : the vessel is 5^ inches high, and 4 f 
inches in diameter ; the tubes are each | of an inch in diameter, and 5 inches deep. 
The materials, being prepared separately in this vessel, were afterwards mixed in a 
wine-glass. 
By means of this apparatus, in one instance, muriate of lime put into one tube, 
in a liquid state, and water in the other, were both consolidated by cold, then ground 
to powder, and afterwards mixed ; but the salt did not grind well, and it moreover 
eroded and rysted the instrument. 
