827 
of Edinburgh, Session 1881-82. 
extent. But he adds, that we must not lay too much stress on 
this conclusion ; for if the decomposition of ammonium salts of 
strong acids is not to he detected by the thermometer, it is in con- 
sequence of its minuteness — for it really exists, and can be made 
evident by other proofs. 
I hope soon to be able to bring forward other and more complete 
proofs of dissociation in the above salts, and also to extend my 
experiments to solutions of other ammonium salts. 
4. On a Solar Calorimeter, and some Observations made with 
it in Upper Egypt. By Mr. J. Y. Buchanan. 
(Abstract.) 
The instrument consists of a Liebig’s condenser mounted equatori- 
ally, so as to follow the sun by one motion. Projecting from the 
upper part of it, and enclosing the steam tube, is the boiler, which 
is a tube of half an inch diameter, where it receives the sun’s rays, 
and widens out to 1 inch diameter in the steam space. This 
steam space or dome is formed by an inverted test tube, so that the 
operation can be easily watched. The tube is surrounded by a 
concave reflector made up of three conical surfaces of silvered 
copper. The diameter of the outer edge of the reflector is 13 -5 
inches, and its effective surface is almost exactly 1 square foot. 
The length of tube on which the rays were concentrated was 2 
inches, and as its diameter was half an inch, its surface was 3*14 
inches, therefore the thermal magnifying power of the combination 
was 46. These proportions were chosen in some doubt as to their 
suitability, but their choice was justified by the result. The amount 
of water actually in the focal portion of the boiler at any moment 
was 5 cubic centimetres; as the steam passed down through a 
central tube, and was condensed by the water rising outside of it to 
supply the place of what was evaporated in the boiler, the supply 
or feed to the boiler was effected practically at the temperature of 
ebullition. When, therefore, the instrument had been working for 
a few minutes, the whole of the effective radiant heat thrown upon 
the boiler was utilised in transforming water at 212° F. into steam 
of the same temperature. As the heat given out in the condensatio 
