THE EXHIBITION OE 1862- 
59 
portant commercial products are manufactured from materials 
formerly thrown away., and at first sight apparently valueless 
and repulsive. 
Dirt has been aptly defined as being’ valuable matter in the 
wrong place, and it is a striking characteristic of the chemistry 
of the present day that it converts substances, apparently the 
most worthless, into commercial utilities, and even fashionable 
luxuries. The manufactures alluded to above, and those of 
Prussian blue, disinfectants, glue, &c., are striking illustrations 
of this chemical utilization of waste materials, and we shall 
endeavour, in the following remarks, to show how they have all 
sprung into existence by the application of chemical facts and 
principles to such waste materials as gas-water, coal-tar, rags, 
and bones. 
When coal is distilled in close vessels for the purposes of the 
gas manufacturer, various other products are obtained at the 
same time. A large quantity of offensively-smelling water 
comes over •, the various sulphur compounds present in the coal 
yield up this element to the gaseous products, whilst a con- 
siderable bulk of tarry matter is also produced. Now the 
object of the manufacturer being to produce as much gas as 
possible in a practically pure state, all these accessory products 
were for many years looked upon as necessary evils, to be got 
rid of as quickly as possible. The gas-water and tar were 
thrown away into the nearest stream, where they killed the 
fish and poisoned the atmosphere for miles around, whilst the 
sulphur was removed, or at least supposed to be removed 
from the gas by means of lime, or, as more recently adopted, 
through a mixture of sawdust and oxide of iron, about which 
more will be said anon. 
The first of these noxious products, the gas-water, has been 
utilized in the following manner. It owes its bad smell princi- 
pally to the presence of ammonia and sulphur compounds, and 
it is only necessary to add some quicklime to this, for it to 
seize upon the acids with which the ammonia is in combination 
and liberate the alkali. This gas is conducted into chambers 
where it meets with carbonic acid, forming, after appropriate 
purification, the salt known in commerce as carbonate of 
ammonia, about 2,000 tons of which are made annually from 
this liquid. If, instead of distilling the gas-liquor with lime, a 
strong acid is added to it, hydrochloric for instance, itself a 
waste product, the compound known as sal-ammoniac is pro- 
duced, which is of very great value in the arts, being the 
principal source of the more common salts of ammonia met with 
in commerce ; the liquor ammonice of pharmacy, or hartshorn, 
being made by distilling this purified sal-ammoniac with lime, 
and conducting the evolved gas into water. The uses of this 
