108 
PROFESSOR W. RAMSAY AND DR. S. YOUNG 
The dissociation of this substance was evidently far from complete, and it will be 
seen that the curve representing temperatures of volatilization approaches more nearly 
to the usual form of a vapour-pressure curve. The pressure, 280-290 millims., lies 
considerably below that obtained by the still method at 78'25°, which is about 
420 millims., and it is very far below saturation, as indicated by experiments with 
the barometer-tube. 
§ 62. Paraldehyde and Metaldehyde .—It was thought that some results might 
have been obtained from these substances. Paraldehyde is a liquid of the formula 
C 6 H 13 0 3 =3C 3 H 4 0, obtained by treating aldehyde with a minute quantity of sul¬ 
phurous anhydride, cyanogen, or certain other substances. Its vapour-density is 
said to be normal for the formula C 6 H 13 0 3 (Beilstein, ‘ Handbuch der Organischen 
Chemie,’ p. 28). It boils at 124° (Kekule and Zincke), at 123'2° to 123'5° (Bruhl). 
When distilled with a little sulphuric acid it changes totally to aldehyde 
(Weidenbusch). 
A portion boiling at 122 - 6° was employed for the following experiments. When 
heated in a barometer-tube it was found to attack the mercury; it was therefore well 
shaken with mercury and redistilled. The pure substance does not appear to 
decompose, and the results obtained by the two methods were practically identical. 
Metaldehyde is a solid crystalline body, produced by the action of gaseous hydrogen 
chloride, or sulphurous anhydride on aldehyde in a freezing mixture. It is insoluble 
in the ordinary solvents, and sublimes without melting at 112-115°, and when heated 
under pressure to 120° it changes completely into aldehyde. Its dissociation-pressure 
was determined in a barometer-tube. 
Temperature. 
Pressure. 
Time. 
millims. 
17-0 
11-8 
24 hours 
50-4 
282-0 
216’ 
332-0 
216'+ 380'= 596' 
339-4 
596' + 75' = 671' 
The rise of pressure was 2'4 millims. in the last 35'. 
Temperature. 
Pressure. 
Time. 
O 
60 
millims. 
459-0 
335' 
The pressure rose 14’3 millims. in the last 60'. 
We have evidently here to deal with a substance the equilibrium of which is 
established only after a very long time. It was allowed to cool, and stood for ten 
days; combination was gradually taking place, as shown by the gradual rise of the 
mercury. 
