212 



V, for instance can be f'oniul from the amount of solid snbstahce 

 7^ contained in tlie mass and the sp. gr. of the bound liquid. 



In most cases v will occur in ihe formula as a <pmntlty specilic 

 and constant for the materiah If, however, the lixiviation is assisted 

 by pressing' so tiiat during, or after each filtration the "natural" 

 volume V is reduced to v' , v Avili be variable and the result of the 

 lixi\iation be dependent on the value of v'. Hence the formulae found 

 show also the influence of the degree of pressing on the lixiviation. 



T . Because, as we have assumed, this qwintity remains constant 

 during the process, V can be measured as the volume of water 

 added, or as the volume of solution obtidned. In how far the said 

 assumption is correct or not and its eventual influence on the results, 

 must be ascertained for each case. 



tn, li and — [continuous ami semi-continuous). By x-arjing these 

 dt 



f <^i A • , 



quantiiies I in which tu - alwcijs = l„ I we can ascertain the 



inflnence of changes in these quantities on the results of the lixiviation. 



dl 

 It should be observed here that for a definite apparatus — is 



dl 



proportional to the vield. 



1 , 1 



ƒ„, n and Lt {discontinuous). Here t — = n and — is proportional 



to the yield. 



n. When in the discontinuons and semicontinuous lixiviation n is 

 taken very large these two methods of working change into the 

 continuous method, which fact can, moreover, be readily demonstrated 

 mathematically from the formulae found. 



If for a detinite case we calculate &/> (discontinuous) and ^/^(semi- 

 eontiniioiTs) for different values of n we can ascertain, for both 

 methods of working, what is the influence of the value of 7i en U. 

 Uf) and Us then near the value limit Un=rc or Uc (continuous). 

 We have applied this calculation to the following values for KO, 

 I, V and V and Uc which values agree with a case met with in 

 practice. 



K0= 15,6 



t =r 75 (minutes) 

 F =105 (cc. »/„ gr.) 

 V = 88 (cc. «/„ gr.) 

 Uc= 48 



