July 13, 1372.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
35 
being free from those sudden variations of temperature to 
which condensers in the open air are exposed), is, never¬ 
theless, very defective as regards the main work of cool¬ 
ing and condensation, which is indispensable to perfect 
purification. If the gas is not properly cooled in the 
condensers before entering the scrubbers, the absorbent 
power of the water in those vessels is diminished ; while 
if tarry vapour in large quantity is carried forward into 
the scrubbers, the scrubbing material (as sometimes 
.happens) may be suddenly ‘“fouled” to a degree which 
.•seriously affects the purifying action of the apparatus. 
Scrubbers are used in gasworks mainly tor the pur¬ 
pose of taking out, and retaining, the ammonia in the 
gas (a process which is a highly profitable. one for gas 
companies) ; and they also eliminate a considerable por¬ 
tion of the sulphuretted hydrogen impurity. But, be¬ 
sides the ammonia and sulphuretted hydrogen, the 
scrubbers are capable of taking out a large portion of 
the carbonic acid in the gas ; and this is the important 
point here. The portion of the carbonic acid not taken 
cut by the scrubbers, of course, goes forward with the 
gas into the purifiers. Now, in the case of lime puri¬ 
fiers, the entrance of carbonic acid is of all things the 
most detrimental to their action; for it converts the 
lime into carbonate of lime, which has no effect upon the 
sulphur in the gas at all. However large or numerous 
the purifying vessels may be, in so far as the lime con¬ 
tained in them exists in the form of carbonate, they are 
perfectly useless ; and, as already stated, clean lime also 
(though quickly absorbing sulphuretted hydrogen) has 
hardly any action upon sulphur in other form than 
SH 
o* 
These two facts show how it may happen that neither 
magnitude of the purifiers, nor frequent changes of the 
lime, have any corresponding effect in purifying the gas 
from “sulphur,” which has hitherto been the case at 
Beckton. It is only when the lime exists as sulphide of 
calcium that it acts upon “sulphur;” hence the larger 
proportion of lime in the purifiers which can be main¬ 
tained in the form of sulphide of calcium, the more effi¬ 
cient will be the purification from “ sulphur.” 
When the lime is used before the oxide of iron (as 
since August has been the case at Beckton), the sulphu¬ 
retted hydrogen in the gas, if it have a free field to act, 
will speedily and certainly convert the clean lime in the 
purifiers into sulphide of calcium ; but, along with sul¬ 
phuretted hydrogen in the gas, comes carbonic acid, 
which at this stage of purification exists in the gas in 
larger quantity than the sulphuretted hydrogen, and 
which has also a greater affinity for lime than the sul¬ 
phuretted hydrogen has ; consequently, the sulphuretted 
hydrogen can only seize upon that portion of the limo 
in the purifiers which the carbonic acid is not in suffi¬ 
cient quantity to occupy. In this way, only a small 
portion of the lime may be in the form of sulphide, the 
remainder being carbonate. Say that only one-fourth 
of the lime in a purifier exists as sulphide, then a purifier 
of one-fourth the size, if its contents existed wholly in 
the form of sulphide, would do as much work upon the 
■“sulphur” as the larger one. As lime in the form of 
carbonate does not take up sulphur in any form, it fol¬ 
lows that as soon as the remainder of the lime is occu¬ 
pied by the sulphuretted hydrogen, the purifier can take 
up no more sulphuretted hydrogen, and consequently 
becomes “foul,” the sulphuretted hydrogen thereafter 
passing through it unabsorbed. Moreover, carbonic 
.acid, having the greater affinity for lime, as it continues 
to enter the purifier, invades the part of the lime which 
.exists as sulphide, expelling the sulphuretted hydrogen 
from the lime and taking its place ; so that the contents 
,of the entire purifier would ultimately be converted into 
vcarbonate, which, as already said, does not act upon 
.sulphur in any form. Thus a purifier may be “ foul 
without being saturated with sulphuretted hydrogen at 
.all; its contents existing wholly as carbonate of lime, 
.and therefore powerless to absorb sulphur in any form. 
Such an excess of carbonate in the lime-purifiers, pro¬ 
portionately nullifying their action, is unquestionably, 
in the opinion of the referees, the true cause of the recent 
and unexpected failure in this branch of the gas-purifica¬ 
tion at Beckton. 
Careful observations at Beckton show the tempera¬ 
ture of the gas as it enters the scrubbers has averaged 
100 ° F. throughout the past year; whereas in several 
of the London gasworks the temperature at the same 
stage of purification is only 60° or 70° F. Water at the 
temperature of 60° F. (barometer 30 ) is capable of ab¬ 
sorbing 780 times its own volume of ammonia, fully 2£ 
times its volume of sulphuretted hydrogen, and one 
volume of carbonic acid. These figures show that water 
has a lesser affinity for carbonic acid than for the two 
other mentioned gas impurities; so that a very, large 
quantity of ammonia and a considerable quantity of 
sulphuretted hydrogen may be taken up by water when 
the temperature is such that no portion of the carbonic 
acid in the gas is absorbed at all. As heat impaiis the 
absorptive power of the liquor, it is obvious that the 
higher the temperature of the scrubbers the larger will 
be the quantity of carbonic acid (as well as of ammonia 
and sulphuretted hydrogen) which escapes from them 
unabsorbed and passes forward with the gas into the 
purifiers. . , ... c ,, 
Thus, independently of experiments, it is perfectly 
certain that carbonic acid must enter the purifiers 
at Beckton in greater quantity than is usual in gas¬ 
works ; and so far as any testings have been made, these 
testiugs corroborate this most important inference. 
It is therefore evident that wherever lime punfieis aie 
used, it is important above all things to keep out car¬ 
bonic acid. Indeed, the anomaly observable at the 
Bow works, where two lime purifiers m winter are as 
efficient as the whole three are in summer, is probably 
to be accounted for on this ground; the temperature of 
the condensers and scrubbers being lower m.winter than 
in summer, and consequently more carbonic acid (and 
also more sulphur) is taken out of the gas before enter mg 
the purifiers in the former case than in the latter. I fie 
difference also between the kinds of coal which have re¬ 
spectively a good or a bad name as regards “sulphur 
may arise more from the amount of carbonic acid which 
they contain than from the amount of sulphur. . 
The referees think the prime object to be sought is to 
utilize and perfect the existing processes of purification ; 
for, if these can be made to yield satisfactory results, the 
interests of the public require that this should be accom¬ 
plished in preference to the introduction of other pro¬ 
tases which would increase the cost of gas manufacture. 
They feel confident that such a result is attainable. Ex¬ 
periments which they have made show that lime in the 
form of sulphide of calcium (t. e. saturated with sulphu¬ 
retted hydrogen) is a perfectly adequate purifying agent 
for “ sulphur.” In their laboratory experiments, they 
are able in this way to wholly remove the sulphur (about 
26 grains per 100 feet) from the gas supplied to then 
office. So complete a result, of course, cannot be expected 
in gasworks; indeed, even in their laboratory experi 
ments, they found that the purifying power of the mate¬ 
rial decreased on each subsequent day, owing, doubtless, 
to the carbonic acid in the gas (about 1 pei cent.) gia u- 
ally nullifying a portion of the material by converting 
it into carbonate of lime. Nevertheless, making due 
allowance for the difference between laboratory experi¬ 
ments and purification on a manufacturing scale, the 
referees feel assured that perfect results would be ob¬ 
tainable from the lime process of purification if carbonic 
acid were excluded from the purifiers ; and also that the 
result will be adequate to the requirements of the public 
if the carbonic acid which enters the purifiers be kept 
down to the lowest point actually attainable in gas- 
W The problem to be solved is, how to take out all the 
carbonic acid from the gas without simultaneously takin 0 
