Hydraulic lifts are of many forms and sizes, from the small dinner lift to the passenger or luggage elevator. The principles on which they work are very simple, and can be illustrated by a common syringe or squirt. If the nozzle of such an appliance is attached to a cock on a water pipe, a piece of indiarubber tubing will do for making the connection, and the piston or plunger is pushed in as far as it will go before starting. On turning on the water, the piston will be forced outwards, and if stood or held upright a load or weight placed on the top would be raised. The weight of the load it would lift would be in proportion to the pressure of the water in the main and the area of the end of the piston or plunger. If the pressure in the main is say 501b. per square Inch, and the end of the piston an area of 1 sq. in., then 501b. of weight could be balanced. If one-third of the power is absorbed by the friction between the cylinder and the packing or gland, then50x2/3 = 33'31b. equals the load that would be raised, the load in.•hiding the weight of the piston and carriage, ear, or platform upon which the load to be lifted rests.

If the area of the above piston end was equal to 100sq. in., then 100x50x2/2= 3,333.31b. (which is the load piston, cage, etc.) that would be raised.