230 THE CHEMICAL CONTROL OF THE DAIRY. 



To rotate the machine, put the metal end of the catgut intc 

 the hole in the spindle, wind the string around, by turning the 

 disc-plate backwards till the handle is close to the spindle. Pult 

 the handle with full strength, the whole weight of the body being; 

 brought to bear, and as the string unwinds the machine is rotated ; 

 when all the string is unwound the end comes out of the hole, 

 and the machine rotates freely. If clean and well oiled it willl 

 run for ten minutes. 



To stop the machine, take hold of the milled-headed nut of 

 cover firmly and it will screw itself ofi ; then press the edge of 

 the under disc-plate gently with the finger till it stops. Do 

 not stop it with a jerk. 



II. The " Excelsior " Gearing. — This can be fitted tO' 

 8- or 24-sample machines. It consists of a hollow cylinder 

 fixed to the frame carrying a hollow double pulley, inside which 

 the spindle can rotate without touching. Round the lower 

 portion of the pulley is coiled a spring, and in the opposite direc- 

 tion round the upper a strap is wound, which passes through an 

 opening in the cylinder ; on the strap is clamped a stop-plate, 

 which serves a double purpose — (1) to prevent the spring from 

 pulling the strap too far, and (2) to lift the pulley, which is capable 

 of a slight vertical movement, when the strap is wound home. 

 At the bottom of the pulley is a pawl, which when the stop- 

 plate is pulled out, engages a ratchet wheel on the spindle and 

 which is lifted with the pulley when the stop-plate is home, 

 so that the pulley runs freely. The machine is rotated by pulhng 

 the handle on the end of the strap rapidly to and fro fifteen to 

 twenty times, when a high velocity is obtained ; the strap and 

 stop-plate are then allowed to go home and the machine runs 

 alone. If the speed slackens, it can be increased by a few further 

 pulls. This gearing is only recommended for 24-sample machines. 



III. The " Rapid " Gearing. — In this, a loose pulley sur- 

 rounds the spindle ; it runs on a separate bearing and is, when 

 not in use, kept up by a spring. A strap passes round the loose 

 pulley, and when this is pulled (in a slightly downward direction) 

 the pulley is brought downwards ; two bevelled teeth engage 

 two similar teeth on the spindle and cause the machine to rotate. 



When the strap is pulled back (in a slightly upward direction) 

 the spring forces the pulley up and the machine rotates freely. 

 By pulling the strap rapidly backwards and forwards, a high 

 rate of speed can be obtained. 



The 2-bottle machine differs in construction from the others 

 in not having the disc-plates, which are replaced by two arms, 

 carrying cups ; these cups are larger than the cups used in the 

 larger machine and have a cover ; the test bottles fit completely 

 into them and are surrounded by warm water. 



