266 
MESSRS W. N. HARTLEY A YD A. K. HUNTINGTON ON THE ACTION 
4'8 grammes ; acetate, 6‘1 ; propionate, 7'4, and butyrate, 8'7 grammes in each 12c.c. 
of liquid, or the solutions of acetate, propionate, and butyrate contained 50‘8, 61'6, 
and 72 - 5 per cent, of the respective salts. The acetate and propionate formed super¬ 
saturated solutions. 
Single and double thicknesses of liquid were examined. In Diagram No. 2 is shown 
the effect on the ultra-violet rays of the spectrum due to three successive members 
of a homologous series of acids. Each solution contained a molecule of the sodium 
salt of the acid. The two series of observations 1 and 2 represent the action of 
single and double cells or thicknesses of f and 1 f inch respectively. It is particularly 
striking how the second series of observations shows a regular decrease in transmitted 
rays caused by each increment of CH 2 in the molecule. 
The same fact is again noticeable in Diagram No. 3, Plate 23. Here, in order to get 
rid of the inconvenience caused by the change of alkaline formates into oxalates on 
evaporation, we made use of very beautiful specimens of barium salts. In this case 
the formate is the most transparent of salts, and it may be seen that the acetate bears 
the same relation to it in transparency that in the case of the sodium salt the 
propionate bore to the acetate. 
A glance at Diagram No. 3 will show that a cell-full of the acids corresponding to 
the ethylic and propylic alcohols, which we have every reason to believe are perfectly 
pure substances, are less diactinic than the alcohols as shown in Diagram No. 1, which 
fact points to the carboxyl group in the molecule possessing a special absorptive power 
greater than that of hydroxyl. We have further evidence of this in the short 
spectrum of oxalic as compared with acetic acid. The specimen examined was pre¬ 
pared with great care and repeatedly recrystallised. There is every reason to believe 
in its absolute purity. 
The Ethereal Salts of Fatty Acids. 
In examining regular series of formates, acetates, propionates, &c., of the radicles, 
methyl, ethyl, and propyl, it was expected that probably the majority of substances 
would be of such a degree of purity that some relation between their constitution and 
their optical properties would be traceable. About twenty specimens of these com¬ 
pound ethers were obtained from Mr. Kahlbaum ; they varied in quantity according 
to the nature of the substances, but the majority of the specimens weighed 50 grammes. 
They were purified by washing with distilled water and with carbonate of potash ; 
they were dried by standing over fused carbonate of potash, and were subsequently 
distilled. The boiling points of the various specimens examined are given on Diagram 
No. 4. 
It will be seen that it was hopeless to get any result from this examination, many 
of the substances manifestly containing impurities which injured their photographic 
transparency. The only three bodies which appear to be pure are the ethylic acetate, 
