May 20, 1871.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
925 
Specific gravity of vapour 
200 -1- 2(127) 
X -0693 = 227 X '0093 = 15*73. 
(See Ether.) 
Hydrargyrt Iodidum Viride. 
200 parts of metallic mercury are triturated with 
127 parts of iodine, and the combination is assisted 
by moistening with a small quantity of spirit, the use 
of which also prevents the development of heat. In 
the Pharmacopoeia 1 ounce (=137'5 grains) of mer¬ 
cury is employed with 278 grains of iodine; these 
proportions are almost identical with those given 
above, which are the numbers theoretically required. 
The product of the official process is a dull greyish- 
green powder, which is directed to be dried in a dark 
room on filtering paper, without heat. 
This substance is very liable to variation in pro¬ 
perties and composition. 
When prepared according to directions, the green 
powder is a mixture of red or mercuric iodide, mer¬ 
curous iodide and metallic mercury; combination is 
incomplete. But when the trituration is continued, 
mixture becomes yellow, and then assumes the cha¬ 
racter of true mercurous iodide Hgl. It changes in 
colour upon exposure to light, and when heated so 
as to cause sublimation, is resolved for the most part 
into metallic mercury and the red iodide. 
YEAST AND OTHER FERMENTS. 
BY C. A. WATKIXS. 
[Continued from page 908.) 
The action of diastase on starch is so well described in 
all chemical works which treat of the vegetable pro¬ 
ducts, that it seems strange any one should attribute the 
conversion of starch into sugar, during germination, to 
any other cause, without assigning some sound reason. 
Yet, in a popular book by Dr. Carpenter, on ‘Vegetable 
Physiology,’ published a few years ago, he says:— 
“ Starch differs but little from sugar, in chemical com¬ 
position, except in containing one additional proportion 
of carbon. When germination commences, oxygen is 
absorbed by the seed in the substance of which it com¬ 
bines with the carbon that is to be set free from it; and 
a large quantity of carbonic acid is then given forth 
again to the air, whilst in the same proportion, the starch 
is converted into sugar.” 
This implies that the conversion of the starch into 
sugar, and the evolution of C 0 2 gas in germination, are 
the results of the same process ; but if you will refer to 
my diagram, you will see that starch does not contain 
an additional proportion of carbon, as compared with 
sugar, but that it requires two equivalents of HO to 
equal it; and that were one or two equivalents of carbon 
to be oxidized and abstracted, we should not have sugar 
as the result. 
It is a well-known fact that in germination the starch 
is converted into sugar by the diastase, which is probably 
formed from the azotized matters by the vital action of 
the embryo. The oxidation of some of the carbon con¬ 
tained in the seed is more likely to be due to the decom¬ 
position of the sugar and other matters by the growth 
of the embryo, the cells of which appear to me to per¬ 
form chemical functions similar to some of the fungi, for 
at this period of its growth it must be remembered the 
vegetable action is reversed, that it is now living on 
organic compounds and evolving C0 2 gas; whereas, 
when it has expanded its leaves to the light and atmo¬ 
sphere, its food must be reduced to simpler forms before 
it can assimilate it, and it will then construct organic 
compounds and decompose C 0 2 gas, eliminating oxygen. 
Malt contains about -r^^th part of its weight of dia¬ 
stase, and as one part of diastase will convert 2000 parts 
of starch into sugar, it evidently contains a much larger 
quantity than is necessary for the conversion of the re¬ 
maining starch in the grain. This is taken advantage 
of in various ways by distillers, etc., for the purpose of 
conveiding unmalted grain and starch from other sources 
into sugar. 
The action of diastase and other similar soluble fer¬ 
ments is supposed to be instantaneous when the matters 
on which they act are also made soluble. 
As an illustration of this, I will tell you what is done 
at one of the large distilleries in the North. 
Starch and grain are ground into a fine powder and 
put into a mash tun capable of holding several hundred 
quarters, and heated till the starch granules burst, and 
a thick paste is formed. AVhen at the proper tempera¬ 
ture, an infusion of malt is run in and agitated, and in 
about two minutes the whole of this stiff mass becomes 
perfectly fluid, the starch being at once converted into 
sugar by the diastase in the infusion. 
In the instances of fermentation I have brought to 
your notice I have shown only the chemical transforma¬ 
tions of the matters fermented, these changes resulting 
in the rearrangement of the atoms or the molecules of 
which those matters are built up, thereby giving rise to 
entirely new structures. 
The ferments themselves suffer differently, being 
always reduced to the simplest combinations. 
Looking at the result of a fermentation, it would 
appear that the ferment and the matter fermented did 
not enter into combination, but that its transformation 
is due to the force generated in the decomposition of the 
ferment with which it is in contact. It is, however, 
clear that the changes which take place in the two 
substances are collateral, for the same ferment will 
produce various chemical transformations of a substance 
according to the phase of its own decomposition. 
“ Thus diastase, when fresh, converts starch into sugar ; 
if kept for a few days, it converts it into gum instead of 
sugar; while at another period it converts the starch 
first into sugar, and then transforms it into lactic acid.” 
Therefore the transformations always depend on, and 
are relative to, the peculiar changes which take place in 
the ferment. 
The commercial production of vinegar appears to be 
due to the agency of one or more microscopic organisms, 
the mass being called the vinegar plant, which, as I 
have said, is not regarded as a true ferment by chemists, 
and for this reason: all the ferments proper, such as I 
have described, produce the transformations entirely 
within the solutions, receiving nothing from, nor im¬ 
parting anything thereto ; but the conversion of alcohol 
into vinegar is a case of simple oxidation, in winch the 
oxygen is derived from the atmosphere, each equivalent 
of alcohol absorbing four equivalents of oxygen to be¬ 
come acetic acid, according to the following formula :—■ 
C,H 6 0 . 2 + 2 0 
Alcohol. 
C 4 H 4 0 2 + 20 
Aldehyd. 
C 4 H 4 0o + 2HO 
Aldehyd. Water. 
= CJI 3 O 3 + HO 
Acetic Acid. 
In countries where no duty is imposed on the manu¬ 
facture of alcohol, it can be made into vinegar cheaply 
and rapidly. The alcohol diluted with water, and a 
small quantity of some azotized substance added, is 
allowed to trickle over beech shavings placed in a vat, 
so arranged that a current of air circulates freely 
throughout. 
For some days the process goes on very slowly; but 
the shavings become gradually covered with a slimy 
fungus, called mother o. vinegar, and then Rectification 
proceeds much more rapidly. 
Pure dilute alcohol, exposed to the air, undergoes no 
chemical change, and its conversion into vinegar is un¬ 
doubtedly due to some complex action of the growth of 
