BAIRD &L TXTLOCK (LONDON) LTD. 



Whatever oil gets below the piston is immediately picked up through the valve (E), when the piston gets to 

 e bottom of its stroke again. When the piston is at the top of its stroke it is in contact with the valve (o), 

 d lifts (G) J in. off its face, giving a free outlet for the air. But there is so much oil on the piston that a con- 

 lerable quantity of it is forced through the valve at (G), driving all air before it. While the piston is at top of 

 oke the valve cannot close, and the oil at (j) and (K) becomes for the time being all one body, so that no air can 

 ssibly return although the valve is fully open. As the valve (G) is resting on the piston it cannot close until 

 e piston has made J in. of its descent, and consequently oil equal to J in. in depth will have entered the cylinder 

 ady to be discharged behind the air upon the next upstroke. 



With a single-cylinder pump a vacuum within J of a millimetre can readily be obtained. With a double-cylinder 

 mp in series, i.e.. with the second barrel exhausting from the first, a very much higher vacuum can be pro- 

 ed. With a good drying tube, a vacuum with i<fas part of a millimetre (measured on a large M'Leod gauge) 

 s been obtained. 

 L. Oil filling plug ; the oil should fill chamber (K) up to the level of oil plug to the point of overflow. 



3717 



3718 



717 T Air Pump, Geryk, No. o size, patent, with a minimum of work gives a very high degree 

 of efficiency. A serviceable apparatus for all exhaustion experiments. The almost 

 perfect vacuum is maintained for a lengthened period, and the solid valves keep long in 

 order. The pump has a li-in. cylinder by 5-in. stroke, with y-in. plate 



his pump is capable of producing a vacuum within .3 of 1 millimetre as measured by 



the M'Leod gauge. 



INSTRUCTIONS. 



This pump is an entirely new invention, being an air pump upon the hydraulic principle, by which the friction 

 reduced to a minimum, all working joints are liquid-sealed and self-adjusting, all valves are automatic, so that 

 s air meets with no resistance whatever. There is no clearance space, and the suction and delivery of air is 

 solute, however slowly the pump is worked. The liquid used is an oil with the lowest possibly vapour tension, 

 e vacuum obtained being equal to the vapour tension of the oil in vacua. No air will ever leak back through 

 s pump. 



Every stroke must be made from extreme bottom to top of pump, otherwise it is ineffective. 



There must always be sufficient oil in the pump to reach to the level of (N), when a vacuum has been formed 

 d the piston is at half-stroke. To determine whether there is a proper charge of oil in the pump, unscrew at 

 ) after pumping up a partial vacuum, and fill the chamber with oil, then screw top on again. Repeat this after 

 ue further pumping, and the pump will then be charged for good. Never let any water or steam get into the 

 mp, and a hygroscopic substance should always be used in the vacuum receiver to dry the air. 



'18 1 Air Pump, Geryk, No. i, without plate and gauge 



This pump is specially designed for hard work in laboratories. Diameter of cylinder, 2 in. ; stroke, 5 in. 

 supplied with a vacuum plate (8 in. diameter) the extra price will be 26/6. It is so frictionless that a boy 

 n readily work it ; it is always ready for use even if put away for any length of time. 



'19 T Air Pump, Geryk, No. 2, larger size, diameter of cylinder, 2 in. ; stroke, 10 in. . . 



If supplied with a vacuum plate (9 in. diameter) the extra price will be 38/-. Vacuum obtained within .3 

 ' i millimetre less than perfect vacuum as measured by the M'Leod gauge. 



500 



5 15 6 



880 



CHEMICAL AND SCIENTIFIC APPARATUS AND PURE CHEMICALS. 



707 



2 Z 



