374 EXPERIMENTS WITH FERTILISERS [chap, 



stirrer within the hopper box keeps the manure moving 

 down to the delivery chains. 



Again, on a different principle are the well-known 

 broadcast distributors, of which an example made by 

 Messrs J. & R. Wallace, of Castle-Douglas, is shown 

 in Fig. 9. Here the manure is carried in a 

 circular hopper from which it simply falls through 

 two apertures the size of which can be regulated, the 

 manure being kept in motion by stirrers within the 

 hopper. The manure is, however, not allowed to fall 

 direct to the ground, but is intercepted by two 

 horizontal discs with radial ribs, which are kept in 

 rapid revolution by gearing connected with the wheels 

 of the machine. As it reaches these discs the manure 

 is flung rapidly in all directions, and so falls on the 

 ground over a much wider strip than the track of the 

 machine. Machines of this type are cheap, light to 

 drive, and handy, and are very convenient for sowing 

 large acreages of grass land with lime or basic slag. 

 The distribution is, however, not very uniform ; if the 

 manure is a mixture, the heavy particles are thrown 

 further than the light, while the very lightest powders 

 are so beaten up into a dust that they float for a con- 

 siderable distance, especially in a wind ; they are thus 

 unsuited for experimental purposes or any very exact 

 work. 



The question is often raised of how far very small 

 plots, a few yards square, cultivated with all the care 

 and attention given by a good gardener to his plants, 

 or even pots, can be made to serve for experimental 

 work on fertilisers, in place of the ordinary field plots of 

 •^ acre or more. For demonstration purposes they do 

 well enough, but for investigation and local enquiry the 

 very care with which the cultivation is carried out prevent 

 the variations induced by the manures in the constitution 



