TRANSACTIONS OF SECTION B. 737 
acid. He then freed his chlorine gas from hydrochloric acid by washing with 
water, and so obtained it pure. This process possessed two distinct advantages :— 
(1) it yielded a very much larger amount of chlorine from the same amount of 
salt; and (2) the nitric acid, which was used for oxidising the hydrogen in the 
hydrochloric acid, was not lost, because the oxides of nitrogen to which it was 
reduced answered the purpose for which the acid itself had previously been 
employed. But this process was very limited in its application, as it could only 
be worked to the extent to which nitric acid was used in vitriol-making. 
The process has been at work at St. Rollox for over fifty years, and, as far as I 
know, is still in operation there; but I am not aware that it has ever been taken 
up elsewhere. 
Within the last few years, however, several serious attempts have been made 
to give to this process a wider scope by regenerating nitric acid from the nitro- 
sulphuric acid and employing it over and over again to produce chlorine from hydro- 
chloric acid. Quite a number of patents have been taken out for this purpose, all 
employing atmospheric air for reconverting the nitrous oxides into nitric acid, and 
differing mainly in details of apparatus and methods of work, and several of these 
have been put to practical test on a fairly large scale in this neighbourhood, and 
also in Glasgow, Middlesbrough, and elsewhere. As I do not want to keep you 
here the whole afternoon, I bave to draw the line somewhere as to what | shall 
include in this brief history of the manufacture of chlorine, and have had to decide 
to restrict myself to those methods which have actually attained the rank of 
manufacturing processes on a large scale. As none of the processes just referred 
to have attained that position, you will excuse me for not entering into further 
details respecting them. 
Mr. Dunlop’s process only produced a very small portion of the chlorine 
manufactured at that time at St. Rollox, the remainder being made, as before, 
from native manganese and muriatic acid, leaving behind the very offensive waste 
liquors I have mentioned before, which increased from year to year, and became 
more and more difficult to get rid of. The problem of recovering from these liquors 
the manganese in the form of peroxide Mr. Dunlop succeeded in solving in 1655. 
He neutralised the free acid and precipitated the iron present by treating these 
liquors with ground chalk in the cold and settling out, and in later years filter- 
pressing the precipitate, which left him a solution of chloride of manganese, mixed 
only with chloride of calcium. This was treated with a fresh quantity of milk of 
chalk, but this time under pressure in closed vessels provided with agitators and 
heated by steam, under which conditions all the manganese was precipitated as 
carbonate of manganese. This precipitate was filtered off and well drained, and 
was then passed on iron trays mounted on carriages through long chambers, in 
which it was exposed to hot air at a temperature of 300° C., the process being 
practically made continuous, one tray at the one end being taken out of these 
chambers, and a fresh tray being put in at the other end. One passage through 
these chambers sufficed to convert. the carbonate of manganese into peroxide, 
which was used in place of, and in the same way as, the native manganese. 
The whole of the residual liquors made at the large works at St. Rollox have 
been treated by this process with signal success for a long number of years, For 
a short time the process was discontinued in favour of the Weldon process (of 
which I have to speak next); but after two years Dunlop’s process was taken up 
again, and, to the best of my knowledge, it is still in operation to this day. It 
has, however, just like Mr. Dunlop’s first chlorine process, never left the place of its 
birth (St. Rollox), although it was for a period of over ten years without a rival. 
In 1866 Mr. Walter Weldon patented.a modification of a process proposed 
by Mr. William Gossage in 1837 for recovering the manganese that had been 
used in the manufacture of chlorine. Mr. Gossage had proposed to treat the 
residual liquors of this manufacture by lime, and to oxidise the resulting protoxide 
of manganese by bringing it into frequent and intimate contact with atmospheric 
air. This process—and several modifications thereof subsequently patented—had 
been tried in various places without success. Mr. Weldon, however, did succeed 
‘in obtaining a very satisfactory result, possibly—even probably—because, not 
