Iii connection with a conversation on the solutions of 
different salts with which almost all the waters in England 
are contaminated, and the practical evils resulting from these 
impurities to steam-boilers, Mr. Spence stated that various 
means had been adopted, with only partial success, for pre- 
venting incrustation on boilers caused by these impurities. 
For some years he had adopted a simple plan, which is 
perfectly successful, both a.t Goole, where the Aire and Calder 
Canal has a considerable amount of lime salts, and also 
at his Newton works, where the water from the Rochdale 
Canal is not only impregnated with lime salts, but apparently 
also with sulphate or chloride of iron. The plan is as follows: 
On the suction part of the water-pipe by which the boiler is 
supplied, that is, between the force-pump and the canal, a 
small vessel is placed, capable of containing about two gallons 
of water ; a pipe of half an inch diameter, with a stop cock, 
communicates from the water-pipe with this vessel ; every 
day the boiler man puts into this vessel lib. or l|lb., as found 
sufficient, of soda ash, and dissolves it in water in the vessel, 
and then, when pumping into the boiler, turns the small cock, 
and in three or four minutes all the solution is taken up and 
passed through the force-pump into the boiler, and this is 
daily repeated ; the consequence is that not the slightest crust 
forms on the boilers and no chipping is ever required, the 
salts being all decomposed and the earthy and metallic bases 
thrown down as mud, which may be blown off or cleaned 
out periodically, if the boiler is a flued one. These two 
boilers are cleaned monthly, and a broom and shovel are the 
only tools required. The plan is easily adopted, perfectly 
efficient, and very generally applicable. 
Dr. Joule drew attention to the great sacrifice of life by 
steam-boiler explosions. He believed that; in nearly every 
instance, rupture took place simply because the iron, by wear 
or otherwise, had become unable to withstand the ordinary 
working pressure. Various hypotheses set up to account for 
