NOTE ON DEFECTIVE SAMPLES OF POTASH AND SODA-WATER. 
215 
mometer they form the terminations of the upright limbs of a tube bent twice 
at right angles. The old form is unsuitable for a great number of experi¬ 
ments to which the new one is specially applicable. The stop-cock connect¬ 
ing the two limbs of the tube is obviously a very valuable addition to the 
instrument, as by its aid the level of the coloured liquid can be immediately 
adjusted. With the ordinary differential thermometer this adjustment is a 
constant source of trouble. The instrument is well adapted for showing the 
differences in the specific heats of the metals. Thus, let equal weights of 
lead and zinc which have been raised to the temperature of 100° C. by im¬ 
mersion in boiling w r ater be cooled in equal bulks of cold water contained in 
two similar vessels ; then, on placing the bulbs of the thermometer in the 
vessels, the difference between the temperatures produced will be immediately 
indicated by a disturbance of the level of the coloured liquid. But if the two 
weights, instead of being equal, be proportionate to the atomic weights of the 
metals, the equal bulks of water will be equally heated, and the coloured 
liquid will remain at rest. For demonstrating the cooling and heating effects 
of the solution and crystallization of salts; the elevation of the boiling-point 
of water on addition of soluble substances ; the unvarying temperature of the 
vapour produced before and after such addition, and many other results of a 
similar character,—this instrument will be found to possess advantages over 
the thermo-pile usually employed, on account of the little trouble attending 
its manipulation, and also because its indications are very distinct and easy 
of explanation. The instrument exhibited was constructed by Cetti, of Lon¬ 
don. The internal diameter of the bulbs is 55 millimetres, and that of the 
connecting tube 5 millimetres. 
NOTE ON DEFECTIVE SAMPLES OF POTASH AND SODA- 
WATER. 
BY B. S. PROCTOR. 
At the Nottingham meeting of the Conference I drew attention to several 
faulty samples of potash water which I had met with; and, as I have again 
met with equally faulty specimens in a lot which was sent as a sample hamper, 
I think it desirable to draw the attention of the Conference to the subject, 
both as a caution to the members, and with the hope that my occasional 
jottings may stimulate the production of the report on the mineral waters of 
commerce, which has been promised for some time past. 
Soda-water.—A bottle, professing to contain 10 grains of bicarbonate, 
yielded, on evaporation, a residue weighing 4 grains, consisting of bicarbonate 
of soda with lime and organic matter, the latter being sufficient to give the 
residue a decided brown colour. 
Potash-water.—The residue of a bottle weighed only 04 grain, and con¬ 
sisted of carbonate of soda, potash, and lime, and organic matter, the potash 
being present in only very small quantity. The pressure of gas was satis¬ 
factory in both cases. 
It is an indication of a very unsatisfactory state of the aerated water trade 
that of five samples, examined at different times, not one proved to be w T hat 
it ought to be,—and only two of the five were such as I had reason to suspect 
were at fault before the examination was made. In more cases than one I 
should have expected the name of the maker a guarantee of good quality. 
Mr. Carteighe thought that the absence of soda from “ soda-water ” was a generally- 
understood fact. 
Mr. Groves had met with soda-w r ater containing ten grains of soda in a bottle. The 
