Q. Is the furr of kettles an oxide?
A. No; the furr (or deposit of boiling water) is a precipitate of lime and mineral salt, separated from the water by the process of boiling.
Q. Is not this furr of boiling water often dangerous?
A. Yes; especially in tubular boilers, such as those employed in railways.
Q. Why is this furr especially troublesome in railway engines?
A. Because it is a bad conductor of heat; in consequence of which, it hinders the evaporating effect of the fire, and prevents the economy of fuel.
Q. Why is this furr especially dangerous in railway engines?
A. Because when it is deposited in the boilers, they are likely to become over-heated; and then explosion will take place from the sudden generation of highly elastic steam.
Q. Why cannot railway engines be fed with brackish water?
A. Because brackish water contains mineral salt, which makes a much larger deposit of furr, than that which contains only vegetable matter.