TRANSACTIONS OF SECTION B. 773 
A number of details are given in the paper dealing with this point. A great 
advantage of the method is the saving of time, especially where a series of 
determinations of a similar character have to be made. 
7. The Behaviour of the More Stable Oxides at High Temperatures. 
By G. H. Barury, D.Sc., Ph.D., and A. A. Ruan. 
This is a continuation of the work already published on the behaviour of 
oxide of copper. The oxides which have now been submitted to the action of the 
oxidising flame of an oxy-coal-gas jet are the most stable of the oxides of lead— 
bismuth, tin, vanadium, antimony, uranium, molybdenum, and tungsten. Of these, 
vanadium pentoxide, antimony tetroxide, and molybdenum trioxide undergo de- 
composition, yielding respectively vanadium trioxide (which readily oxidises on 
exposure to tetroxide), antimony trioxide, and the blue oxide of molybdenum 
respectively. The other oxides appear to undergo no change of composition, 
excepting in the case of tin, where a slight loss of oxygen occurs. 
8. The Spectra of the Haloid Salts of Didymiwm. 
By G. H. Baitey, D.Sc., Ph.D. 
The observations, of which a 7éswmé is given, were commenced some years ago, 
and a communication made upon the earliest results at the Southport Meeting by 
Professor Schuster, in conjunction with the present author. The observations made 
may be classified into qualitative and quantitative, according as they deal with a 
change in the appearance of the absorption-bands, or in their position, 
Crystals of the chloride having been prepared, they were subjected to examina- 
tion, under ordinary light and under polarised light, in such a way that the plane 
of polarisation was parallel to the ortho- and klino-diagonal of the crystal re- 
spectively. No change in the position of the bands was observed, but there were 
marked differences in intensity of several of the bands under each of these condi- 
tions. In like manner, the effect of the presence of reagents in solutions of the 
salts on the position or character of tle bands was studied. Nitric acid was found 
to increase the intensity of certain bands and diminish that of others; so that in its 
presence the character of the spectra is much altered. Other strong acids had 
little effect. Thus far the results are of a qualitative nature. When, however, 
a comparison was made of the spectra of the chloride, bromide, and iodide of 
didymium, it was found that the bands of these salts presented a general similarity 
in character, but occupied different positions : those of the bromide being nearer the 
red, and those of the iodide being nearer the violet, than in the case of the chloride. 
Moreover, the bands of the solution of the chloride were displaced to the 
violet side of the crystal, so that they occupied approximately the same position as 
those of the crystalline iodide. Finally, equal displacement of all the bands did 
not occur ; and there appeared in these quantitative measurements, as also in the 
case where nitric acid was added, a selective action, so that certain bands underwent 
greater displacement or alteration than others, These point to the compound nature 
of didymium, and show some relation to its proximate constituents, praseo- and 
neo-didymium. 
9. On the Condition of the Air in Public Places of Amusement, with special 
reference to Theatre Hygiene. By W. Herwortu Coxtins, £.C.8., 
F.R.M.S. 
The principal theatres in Manchester were taken as types of well-arranged 
English theatres. Samples of air were taken at stated periods during the perform- 
ances in the months of December 1889 and January 1890. Duplicate samples 
were analysed in all cases, and samples of the air outside the theatre were taken 
simultaneously for the purpose of comparison. The examination of the samples 
was confined to the estimation of—(1) carbonic acid (by Pettenkofer’s method) ; 
(2) organic matter (by Carnelley’s method, ‘Proc. Roy. Soe,’ xli. 238); and 
