534 



Bulletin 78. 



ira, 





end of the piston, and the lower end is pointed and works closely in the 

 lower small cylinder only at the point opposite ^. The reser- 

 voir is filled through the opening at e, which is protected by a 

 screw cap. In B, the instrument is ready for insertion in the 

 soil. At A, is shown a section of the lower portion of the instru- 

 ment, nearly one half natural size, and this view represents the 

 position of the valves, v, when the instrument is being with- 

 drawn from the soil. It operates very simply. When the pis- 

 ton is pulled up it is stopped at the proper point by the metal 

 pin through the piston near />, in b. This brings the upper 

 valve into the reservoir, r, and the liquid immediately fills 

 the chamber between the two valves ; this is the measuring 

 chamber, and its size can be easily regulated to hold a tea- 

 spoonful, or more or less, by simply screwing the valves either 

 way or by winding cloth around the piston between the .valves. 

 Before inserting in the soil, the piston is pushed down and is 

 stopped by the lower valve striking against the bottom of its cyl- 

 inder. The valves are then in the position shown in b. As the 

 lower portion of this valve cylinder is cutout larger, the liquid 

 escapes into this lower chamber, /. c, and some runs down 

 around the lower part of the piston but is prevented from escap- 

 ing by the arrangement near the point, at g, by which the piston 

 here fits very closel}^. The pulling up of the piston again, of 

 course, lets the charge of liquid run out, and at the same time 

 the measuring chamber is again filled, thus securing an automa- 

 tic action. It was found necessary to have an opening in the 

 lower chamber, /. r., in order to allow air to take the place of 

 the liquid so it could freely run into the 



soil. This opening, c, also supplies the | 



measuring chamber with air which is 

 drawn up into the reservoir and then dis- 

 places the liquid and allows it to freely en- 

 ter the measuring chamber. All parts 

 of the instrument are made of brass, except 

 the small discs or leather in the valves, and 

 the wooden handle on the piston ; the 

 reservoir may be made of tin. All parts 

 must fit closely, for the liquid works 

 through where water would not. The 

 reservoir can be made larger or smaller, 

 and the lower portion which is inserted 

 in the ground can be made of any length 

 to suit the depth to which it may some- 

 times be necessary to apply the liquid. 

 On larger instruments a foot-rest could Vio.^i.-The McGowenhtjedor. 



