TRANSACTIONS OF SECTION B. 991 
present give up their water and become anhydrous, The author has now satisfied 
himself by experiment that this decomposition or dissociation is progressive and 
does not take place per saltum. Taking sulphate of sodium, which has its point of 
maximum solubility at 34° and above that point deposits the anhydrous salt, he 
has made determinations of the rate of cooling of a strong solution and finds the 
time-temperature curve to be parallel with that of water done under the same con- 
ditions. Calorimetric determinations of the heat of solution of the anhydrous salt 
at successive temperatures lead to the same conclusion, 
11. On the Molecular Constitution of a Solution of Cobaltous Chloride. 
By Professor W. J. Russrtt, Ph.D., F.R.S. 
A thin layer of cobaltous chloride gives an absorption spectrum consisting of 
two broad ill-defined bands. If the chloride be fused with potassium, sodium, or 
calcium chloride, the spectrum of these mixtures, both in the solid and fused 
state, is different from that of cobaltous chloride, alone and consists essentially of four 
bands, two of which are marked and characteristic. This same spectrum is obtained 
with solutions of cobaltous chloride in absolute alcohol, in amy] alcohol, in hydro- 
chloric acid, and in glacial acetic acid. This spectrum would, therefore, appear to 
be that of cobaltous chloride in an altered molecular state. The spectrum of an 
aqueous solution is again different, and consists of one broad band nearer to 
the blue end than the other bands, but the addition of cobaltous chloride to such 
a solution, or of such bodies as possess an affinity for water, causes a reversion of 
the spectrum to that of the anhydrous cobaltous chloride. Heat also produces 
the same effect, and it would appear from these results that the anhydrous chloride 
can exist in aqueous solutions. The changes in the character of a spectrum of 
an aqueous solution produced by heat may be explained as arising from a disso- 
ciation of some of the hydrates existing in the solution, and the production of 
anhydrous cobaltous chloride. Further, the fact that those solutions containing 
the anhydrous salt more readily transmit the blue rays and absorb the red rays, 
whilst those containing hydrates in solution more readily transmit the red rays, 
would indicate that the molecule of the hydrate is smaller than that of the anhy- 
drous salt. The action of water on the anhydrous salt, therefore, is not to form an 
additive compound, but to split the molecule of the anhydrous salt and form one 
in which water replaces cobaltous chloride. 
WEDNESDAY, SEPTEMBER 16. 
The following Papers were read :— 
1. An Electro-centrifugal Machine for Laboratory use.' 
By ALEXANDER Watt, F.L.C., F.C.8. 
This instrument, although in itself possessing no scientific interest, has been 
found so useful in the laboratory as to justify the hope that a description of it 
and a demonstration of its use may prove of interest. 
The late Dr. Mohr, of Bonn, in his ‘ Titrirmethode’ advocated the use of a 
centrifugal machine for the rapid drying of crystalline precipitates, for use in 
volumetric analysis, and although they are admirably adapted for such purposes, 
centrifugal machines are seldom seen in our chemical laboratories. It is possible 
that the neglect of this valuable addition to our laboratory apparatus is owing to 
the inconvenience involved in driving the machine at a high speed by means of the 
ordinary pulleys or other speed-increasing gear, especially when the rotation has 
to be kept up for a considerable length of time. 
1 Printed in full in the Chem. News, vol. 52, p. 232. 
