844 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[April 2G, 1873. 
a certain equilibrium. The proportions of this equi¬ 
librium do not appear to be affected by temperature, 
at least if it be not such as to produce new com¬ 
pounds, as ordinary ether or olefiant gas. In fact, 
the limit of the reaction (with equivalent quantities) 
in the cold, after some weeks, being 59 per cent, of 
sulphovinic acid, I have found 56 per cent, after a 
few. hours. Although the absolute sameness of these 
limits has not been established, because of the slow 
formation of ordinary ether, yet the analogy of the 
ethers formed by organic acids and the preceding 
figures tend to show their identity. 
The limit of equilibrium,—that is to say, the pro¬ 
portion ol sulphovinic acid,—is also modified by the 
relative proportions of the four bodies. Water, in 
particular, after a time decomposes sulphovinic acid. 
Consequently the presence of an excess of water at 
starting lowers the limit of etherification ; it also 
retards the combination. This is shown by the fol¬ 
lowing figures:— 
Per cent, of Sulphuric Acid 
etherified after a contact of 
Nature of Mixture. 
S0 4 H 4 - c 4 h 6 o 2 + §ho* 
S0 4 H + C 4 H 6 0 2 + lgHO 
40 
90 
20 
147 
hours. 
hours. 
days. 
days. 
56-0 
57-4 
59-0 
58-8 
13-2 
21-2 
41*2 
54*8 
Alcohol containing 25 per cent, of water yielded, 
at the end of a month, only 8 per cent, of sulpho¬ 
vinic acid, showing that the presence of water is an ob¬ 
stacle to the combination of the sulphuric acid with 
the alcohol. 
. On the other hand, if water be added to sulpho¬ 
vinic acid, or to a sulphovinate, there is decomposi¬ 
tion and reproduction of alcohol and acid, slowly in 
the cold, rapidly at 100°C.,—in all cases inevitable, 
—until the equilibrium is established between the 
opposing actions. These are the principal facts in the 
preparation and preservation of the sulpliovinates. 
Finally, it may be remarked that sulpliovinates 
are more slowly decomposed in solution than sul¬ 
phovinic acid. It is in consequence of this slowness 
that solutions of sulpliovinates can be evaporated to 
crystallization without being spoiled. But the salt 
should not be kept too long in a state of solution. 
The decomposition of sulpliovinates in solution 
presents a peculiar feature which is worth pointing 
out, namely, that when once commenced it is gra¬ 
dually accelerated. The resulting sulphuric acid 
takes up an equivalent portion of the base and sets 
free an equivalent portion of sulphovinic acid, and 
this latter is much more rapidly decomposed by water 
than the neutral sulpliovinates. In the evaporation, 
the alcohol being given off, each equivalent of sul¬ 
phovinic acid releases two equivalents of free sul¬ 
phuric acid; two equivalents of sulphovinic acid 
quickly result from the reaction of this sulphuric 
acid upon the dissolved sulphovinate, and they in 
their turn are changed by the action of water "into 
four equivalents of free sulphuric acid : the reaction 
once commenced being thus accelerated in geome¬ 
trical progression. 
These phenomena occur as well during evapora¬ 
tion by heat as a simple keeping of a solution ; 
more slowly, indeed, in the latter case, but always 
certain. Hence the utility of maintaining solutions 
of sulpliovinates either in a neutral state or slightly 
alkaline during evaporation or preservation ; this 
* Concentrated acid is here taken, which usually contains 
one-third or more of water. 
may be done by adding to the solution a little neu¬ 
tral carbonate or bicarbonate, which will remain in 
the mother-liquors after crystallization. The pre¬ 
sence of the alkaline salt retards the decomposition, 
without, however, preventing it altogether. 
I do not know whether the neutral sulphovinate, 
once isolated in a crystalline state, can be preserved. 
At ordinary temperatures, if the crystals were anhy¬ 
drous, free from water of crystallization, perhaps it 
might be. But hitherto this result has not been 
attained. All the known sulpliovinates contain water 
of crystallization; and I have found that they all 
undergo change after a longer or shorter time, some¬ 
times after even years. 
The alteration always progresses in the same man¬ 
ner ; some of the crystals commence to effloresce ; 
they become acid, and the whole mass then quickly 
undergoes decomposition. The mechanism of this 
alteration appears to result from the chemical action 
of water; it is due to a commencement of separation, 
however slight it may be, of the water of crystalliza¬ 
tion from the salt which is eliminated by efflores¬ 
cence. While the crystals preserve their chemical 
nature and solid state intact they are stable ; but the 
least trace of water of crystallization separated by 
efflorescence attacks the neighbouring crystals; after 
a certain time it there sets sulphuric acid free and 
leads to the cycle of successive decompositions de¬ 
scribed in connection with solutions. I do not think 
this fatal cycle can be avoided .completely; but it 
can evidently be retarded by only preserving crystals- 
which are well freed from the mother-liquors, and 
keeping them in a place having an invariable tem¬ 
perature. 
HEW SOURCES OF ETHYL- AND METHYL-AHILINE. 
BY JOHN SPIELER, F.C.S.* 
In the process of manufacturing the Hofmann violet by 
the action of ethylic or methylic iodide upon rosaniline or 
one of its salts, there is always produced a considerable, 
quantity of a dark-coloured resinous or pitch-like sub¬ 
stance, which has received the name of “Hofmann gum.” 
This by-product varies in amount and consistence accord¬ 
ing to the shade of violet simultaneously produced, being 
much more abundant when the iodide is employed in large 
proportion for the purpose of obtaining the bluer shades. 
It has hitherto received no technical application, but accu¬ 
mulates as a waste-refuse in the Aniline Dye-Works 
■where Dr. A. W. Hofmann’s process is used. 
Whether obtained by the ethylic or methylic reaction, 
the properties of this body may be briefly summarized as 
follows :—It is easily fusible in boiling water, and very 
nearly of the same gravity, for it sinks or swims with the 
slightest current, being itself all but insoluble in that 
liquid. In dilute acids (sulphuric and hydrochloric) it is 
freely soluble, giving dark-brown liquids, from which the- 
gum may be again thrown down unchanged by neutraliz¬ 
ing with alkali. Alcohol and benzol dissolve it freely, 
especially when heated to nearly the boiling temperature j 
and glacial acetic acid likewise holds it in solution, being 
precipitated, however, on dilution with water. 
During the past year a great number of experiments 
have been made upon various descriptions of Hofmann 
gum, varying in their origin and quality according to the 
amount and nature of the iodide concerned in their pro¬ 
duction. The results naturally divide themselves into two 
series, according as they happen to be ethyl or methyl 
derivatives, but there appears to be a perfect parallel be¬ 
tween the two cases ; and as much interest attaches just 
now to the economical production of methyl-aniline, the 
# From the Proceedings of the Royal Society. 
