Vol. XI. No. 271. 



THE AGRICULTURAL NEWS. 



291 



ground between and under the plants, the early 

 destruction of all cotton plants as soon as the crop is 

 harvested, and also the complete removal and destruc- 

 tion by burning of all weeds, rubbish and cornstalks 

 which would furnish hiding places in which the boll 

 weevils might hibernate.still further reduce the severity 

 of the attacks In addition, a system of rotation has 

 been de\ised which is in use in many places, and this 

 often results in a diversification of crops which is most 

 beneficial. By these means, the Southern farmers arc 

 able to grow profitable crops of cotton in spite of a most 

 serious pest, and they will ultimately gain an advan- 

 tage as a result of the changes in method, that they 

 arc being forced to adopt, which will probably be 

 greater than the losses which they at first experienced. 



All these examples are of the greatest interest on 

 account of their direct value. Sume of them are 

 useful, further, in that they serve to afford 

 instances where, although the degree of success first 

 anticipated has not been attained, the bold con- 

 tinuation of the work has proved to be of incom- 

 parable benefit and has ofcen brought about salut:iry 

 changes in methods which, probably, could not have 

 been caused to accrue in any other way. 



THE RELATION BETWEEN THE CRUSH- 

 ING OF CANE AND THE VOLUME 

 OF THE FIBRE. 



A summary of the conclusion.s from an investiga- 

 tion of this matter is thus given in Bulletin No. 3S, 

 Agricultural and Chemical Series, Experiment Station 

 of the Hawaiian Sug.ir Planters Association, by Noel 

 Deerr: — 



(1) The amount of juice expressed from chopped cane 

 subjected to a direct pressure iacreases with the degree of 

 fineness of the material. 



(2) After chopped cane has been pressed to a certain 

 pressure, a further notable quantity of juice can be obtained 

 by releasing the residue from pressure and pressing again. 



(3) The pressure at which juice begins to flow from 

 megass is not a measure of the pressure at which it has been 

 pressed. 



(4) With the pressure remaining constant, greater 

 percentages of juice are obtained from chopped cane as the 

 quantity of material under pressure decreases. 



(5) With chopped cane the sum of the volumes of 

 e.xpressed juice and residue remains constant 



(6) At pressures up to 60 tt). per square inch the 

 volume of megass varies inversely as the 2' 5th root of the 

 pressure. 



(7) At pressures from -500 Bo. per square inch to 

 12,000 lb. per square inch the volume of megass varies 

 inversely as the 5th root of the pressure. 



(8) The quantity of juice obtained from chopped 

 cane varies as the 12th root of the pressure. 



(9) It is not to be supposed that the relations formu- 

 lated in 6, 7 and 8 above are of the same degree of exactness 

 as the PV = C' law for gases [the product of the pressure 

 and the volume of a gas, at a given temperature, is a con- 

 stant] or any fundamental physical law: actually the e.xponent 

 in the equations increases as a function of the pressure: at 

 the higher pressures the increase is however very slow, and 

 the simpler expression may be used to develop a theory of 

 the strains and stresses in the three-roller mill. 



(10) The pressure exerted by the layer of megass in its 

 passage between the top and front roller of a standard three- 

 roller mill is small compared with that exerted in its passage 

 between the top and back roller, and probably amounts to 

 about one-fortieth, with settings such are in common use. 



(11) The line of no side thrust in a three-roller mill of 

 standard design is only a little deflected from the line 

 joining the centres of the top and back rollers. 



(12) From consideration of the equation Hn P = C 

 [where H is the height of the column of megass under 

 pressure, n the number of mills and P the pressure], the 

 pressure on the trash turner, the power therein absorbed, 

 the pressure on the rollers, the power required to compress 

 megass, etc , can be calculated either by analytical or by 

 graphic methods. It is to be distinctly understood that all 

 these calculations are relative and that the accuracy of the 

 numerical results arrived at depends on the accurate deter 

 mination of the value of H^ P for one particular set of 

 conditions; in other words, 'if the power required to com- 

 press t tons of filire in one hour to a volume V is p, then the 

 power required to compress t' tons of fibre in one hour to 

 a volume Y is p' as deduced from consideration of the 

 equation of H" P = CV 



(13) It has been shown (in the preceding pages) that the 

 pressure exerted by the megass in its passage between the 

 top and front roller is very much less — probably about 

 one fortieth — than than exerted in its passage between the 

 top and back roller, that is to say, the strain in the conven- 

 tional three-roller mill is symmetrical and as much metal is 

 used in the feed side and in the front roller as in the 

 delivery side and in the back roller. The logical application 

 of the experiments described here would indicate that the 

 front roller be regarded solely as a feed roller and would 

 point to a two-roller mill with a small feed roller as being 

 the rational design for the later mills of a train. 



In a two-roller mill, however, the pressure exerted by 

 the layer of megass will not be in a vertical line, but following 

 the construction given will pass through a point 810 inch 

 from the line of nearest approach of the rollers; in a mill 

 with rollers superimposed vertically there will then be 

 a small side thrust, due to the slow recovery of megass after 

 compression. 



DEPARTMENT NEWS. 



The Imperial Commissioner of Agriculture left 

 Barbados by the S.S. 'Oruro', on August 30, 1912, for 

 the purpose of making an ofKcial visit to St. Vincent. 

 Dr. Watts was expected to return to Barbados by the 

 S.S. 'Ocamo', on September 14. 



Mr. F. Birkinshaw, of Kew, has been appointed by 

 the Secretary of State for the Colonies to the post of 

 Assistant Agricultural Superintendent, St. Vincent. 

 Mr. Birkinshaw arrived in St. Vincent, to take up the 

 duties of hi.s appointment, on August 28.. 



