_To properly use a hydraulic jack._ Place the head under the weight to be raised, be careful to set the jack plumb with a good solid footing; put the lever into the socket with its projection on the bottom side; work the lever until the weight has been raised to the desired height _or an escape of liquid blows out of the safety vent_. Hold the lever up or raise it to its highest position and remove it from the socket to prevent the valve from opening. In lowering insert the lever in the socket with the projection underneath and then cautiously press it slowly down until it brings up against the stop; remove the lever and turn it over with the projection on top; insert the lever in the socket and gently but firmly press it on the end with the right hand clasping the ram with the fore finger, and thumb of the left hand: thus the workman has full control of the jack and can lower and stop as frequently as may be found necessary. If from any cause the valves stick a few sharp quick strokes of the lever will usually release it and cause it to work, if not, it should be thoroughly cleaned. Before shipping the brass filling screw should always be screwed down tight, and before using this screw should always be loosened to let the air out and in. NOTE.—A prominent firm making these tools says: “In our Jacks, rams are cut and cylinders bored from solid high carbon steel. We have nearly 300 styles for pushing, pulling or lifting.” This shows the wide use to which hydraulic jacks are put; the style shown in the Glossary with its broad base is to be used when the jack stands upon a light board on the ground and can be placed under the work, or where steadiness is required. Fig. 139 shows a style to be used when there is not room enough to get the head of the jack under the work, and is the style generally used for moving engines, boilers, machinery, etc. _In repairing hydraulic jacks_ the following points should be carefully observed; before attempting to repair a hydraulic jack the trouble should be definitely located, next: Put the jack under a weight and attempt to raise it, carefully watching its action. Should the liquid leak out around the lever socket, the gland should be tightened slightly until this leak disappears. If the packing is worn out unscrew the set screw at the back of the head about one-quarter inch, then withdraw the socket not more than one inch, unscrew the gland and put in a new packing of lamp wick braided and well oiled with mineral oil, which is free from gum. Afterwards put the socket back to its former place and tighten the set screw. When the pump valve leaks the lever can be worked up and down without raising the ram. This is also true when the plunger packing becomes worn. If the trouble is found with the valve it can be ground by taking out the pump plug and unscrewing the brass bonnet which covers the valve. [Illustration: FIG. 139.]