TREATMENT OF STEAM.

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the back of the boiler, and the great heat at this part soon cracks theplate, if the scale that rapidly forms is not frequently removed. Ofcourse, where water from a surfäce-condenser is used, little or nodeposit is formed over the heating surfaces; but even with surface-condenser water, it is found necessary to allow a slight film ofdeposit to form, otherwise the corrosion that rapidly sets in wouldcorrode the plates very quickly. As we cannot prevent the waterfrothing up when it is taken into the boiler in an impure state,we must simply consider the best means to prevent the water primingover into the cylinders. With a good height of steam-chest, andwith the steam taken from the highest point, the bubbles of waterwill be broken up before reaching the top of the inside steam-pipein the boiler, and when a slotted pipe is carried along the top ofthe boiler, perforated with a number of slits inch wide, should theglobules of steam and water reach that height, as they cannot passthrough the slits, they are broken up, liberating the steam, whichfinds its way through the slits into the pipe, while the water con-tained in the spheres falls down amongst the water in the boiler,with the additional advantage that the steam is taken away directlyfrom over the surfaces where it is generated. However, when nopriming takes place, a certain amount of water will be carried alongwith the steam; and when the steam-pipe is at one point, the atomsare all converging to that point, and the mere mechanical frictionof the atoms of steam rubbing against one another tends to carrywater through the steam-pipe into the cylinders, therefore the steamshould be partially dried by an apparatus we will now explain.

TREATMENT OF STEAM FROM THE BOILER TOTHE CYLINDER.

Steam generated from ordinary boilers is far from being a puregas, properly speaking, it is quite dry and invisible. The vapourblowing off from the safety-valve shows a transparent ring near theorifice of the valve; this ring, however, soon widens, and mixingwith the cold atmosphere, takes the form of a misty vapour, highlycharged with watery particles; this vapour is soon dispelled, and