776 REPORT—1890. 
their works, occupied by highly-skilled chemists, would raise the chemical industries 
of the country to the highest state of perfection. 
3. Behaviour of Copper Potassium Chloride and its Aqueous Solutions at 
different Temperatures. By J. H. Van ’t Horr. 
When the blue crystalline double chloride of copper and potassium (CuCl,, 
2KCl, 2H,0) is heated to 100° C. it changes colour, and can be seen to be decom- 
posed into three constituents—water, small cubical crystals of potassium chloride, 
and reddish-brown needles of a new double salt (CuCl,, KCl), This double salt 
may also be prepared by gently heating the blue double salt with excess of cupric 
chloride ; thus :— 
CuCl,, 2KCl, 2H,0 + CuCl,, 2H,O = 2CuCl,K + 4H,0. 
Both these changes are reversible, and take place at fixed temperatures, which were 
determined by noting the change of volume of the mixtures in a dilatometer. The 
first change was found to take place at 98°C., the second at 56°C. 
The solubility of all the salts concerned was carefully examined, and the vapour- 
pressures of the different solutions were determined simultaneously in a manometer 
with four branches. 
A, Report of the Committee on the Action of Light on the Hydracids of 
the Halogens in presence of Oxygen.—See Reports, p. 263. 
5. Experiments on the Combustion of Gases wider Pressure. By Professor 
Liveine, F.R.S., and Professor Dewan, F.R.S. 
6. On the Rate of Explosion of Hydrogen and Chlorine in the Dry and Moist 
States.' By Professor H. B. Dixon, F.2.8., and J. A. Harker. 
The authors have previously shown (confirming Pringsheim’s experiments) that 
a mixture of hydrogen and chlorine in a thoroughly dried state is far less sensitive 
to explosion by light than when the gases are moist. The authors have now 
determined the rate of the ‘ explosion-wave’ of hydrogen and chlorine in the dried 
and in the moist states. The gases were fired by an electric spark, and the measure- 
ment was begun at a distance of 4 feet from the firing-point. The mean rate 
for the dried gases is slightly faster than that for the moist gases, a fact which 
points to the direct combination of hydrogen and chlorine under these conditions 
without the interaction of water. 
7. On the Ignition of Explosive Gaseous Mixtures. 
By G. 8. Turrin, B.A., D.Sc. 
The author has commenced a thorough investigation of the conditions affecting 
the ignition of explosive mixtures of gases, and the present paper gives an account 
of the results obtained in a series of experiments on the temperatures of ignition of 
various mixtures of OS, vapour with oxygen and other gases. 
Davy was the earliest investigator of the subject, but his method, which was to 
observe the effect of plunging a heated rod of iron into a jar containing the gaseous 
mixture, could not lead to any definite results. This same method was afterwards 
applied by Frankland, and, with considerable improvements, by Wiillner and O. 
Lehmann. A far better apparatus was described by A. Mitscherlich in 1877, but 
apparently ke did not carry out the investigation he had planned. The principle 
ef this apparatus is the same as the first one used by Mallard and Le Chatelier a 
1 Published in eatenso in the Memoirs of the Marchester Lit. and Phil. Soc., 1890-1. 
