26 Dr. Playfair’s Lecture on the Great Exhibition of 1851. 
oughly comprehended by science, and consequently has not de- 
ived so many advantages from its application. 
reater acquaintance with the theory of bleaching has led 
to a better understanding of the very ancient practice of washing. 
The washing of domestic linen is by no means an operation too 
insignificant for the attention of the chemist. A dozen shirts 
may cost 3/. 12s., this being the united interest of the producer, 
cotton-spinner, and shirt-maker. These shirts will last three 
years, with care, and supposing three to be washed each week, 
the cost of washing—that is, the washerwomen’s interest in the 
dozen shirts—amounts‘to 7/. 16s., or more than double that of 
the cotton-spinner. In fact, the cost of washing is about one- 
twelfth the income of a family of moderate means. Taking 
rich and poor together, and estimating the cost of washing at no 
more than 3d. per head weekly, the annual charge of washing 
to the metropolis alone is 1,535,060/., which is equal to about 
one-twenty-fifth of the whole capital invested in the cotton man- 
ufactures of the United Kingdom. Hard water usually contains 
lime, and in washing that earth unites with the fatty acid of 
soap, producing an insoluble body of no use as a detergent. For 
every 100 gallons of Thames water, 30 oz. of soap. are thus 
wasted, before a detergent lather is formed. In personal ablution, 
we economize this excessive waste by the uncomfortable practice, 
universally followed in London, of taking about an ounce o 
water into the hands, and converting it into a lather, the water 
in the basin being only employed to rinse this off, instead of aid- 
ing in the detergence. But in washing linen this plan cannot be 
followed, every particle of the lime being removed before the 
soap becomes useful ; this, as a matter of economy, is frequently 
accomplished by carbonate of soda, as being cheaper than soap, 
The amount of soap and soda salt thus wasted in the metropolis 
has been stated to be equal to the gross water rental. Hard 
water, besides wasting soap, produces a great tear and wear of 
clothes. 
All these facts are well known to manufacturers, and hence 
the care with which a water is selected before the seat of a mau- 
ufactory is determined. Wh , then, should we not attend to 
our domestic manufactures, considered’ trifling only because they 
gate? Yet these domestic manufactures are of more impor- 
tance, economically, than those carried on in large and imposing 
factories. ini 
T wish I had time to refer, with sufficient detail, to the discov- 
ery of Mercer, who has shown that the immersion of cotton in 
soda or in sulphuric acid causes an equal contraction of the fibres, 
thus producing the mechanical effect of a loom. If very fine 
calico, containing as much as 180 picks to the inch, be thus 
| 
. 
) 
: 
