The head of the boiler is connected by a pipe _B_ and collar _b_ to the steam inlet pipe _I_ of the steaming vat, heretofore described, as by the collars _b i_. A filling tube _C_ enters the boiler and projects nearly to the bottom, and the water outlet-pipe _F_ with cock _f_ leads off from the upper water line. The tube _C_ forms also a safety valve, for if the steam pressure becomes too great in the boiler and connected vat, it will force water up and out through the tube. If, however, the water falls below the level of the lower end of the tube, steam will issue and warn the attendant that water is too low. It would be best however, to provide a steam gauge, whereby the pressure of steam in the boiler and vat could be accurately indicated. [Illustration: FIG. 43.--Steam Generator.] It is to be noted that when steamed the potatoes will swell and occupy more space and that the steam vat should therefore not be much more than two-thirds filled with potatoes. With the steaming vat above shown, the potatoes are delivered mixed with a considerable quantity of water, but a better plan is to have a perforated false bottom to the tub, whereby the condensed water may be carried away, the steamed potatoes remaining behind. [Illustration: FIG. 44.--Potato Steamer and Crusher.] Two hours of steaming should reduce the potatoes to proper condition, which may be tested by introducing a pointed iron rod through a suitable aperture, normally kept closed. If the rod passes freely inward, the potatoes are done and may be discharged into the crusher, shown in Fig. 44. In this Fig. the steaming vat _A_ is shown mounted above the crusher. A pipe _B_ with cock _b_ leads to the steam generator. The steamed potatoes are shoveled out through the door _a_, which is usually held closed by means of the clamps or buttons _a¥ a¥¥_. =The crusher= consists of a hopper _C_ whose bottom fits closely against two adjacent smooth faced rolls _H I_ of iron. These are driven by gears _D E_. The shafts of these gears have cranks _d d_ whereby it may be operated. These gears are unequal so that the rolls shall move at different speeds, and thus one will have a grinding action against the face of the other. A counter weighted scraper _e_ bears against the face of the roll. The crushed potato pulp passes between the rolls and into a bin beneath, having adjustable walls made of boards _F_, sliding in suitable guides _f_, from which the pulp may be shoveled into the mashing tank or "back." The crusher might, however, be arranged to deliver immediately into the mashing tank, if the latter is provided with means for stirring the delivered pulp.