THE FUSING POINT. 29 



Divide 'the sum of tlie two products by the sum of the 

 percentage of the two constituents ; or in formula : — 

 I" heing fat, and S sinking point, 



Fi + F, 



Example 1. — ^Calculate the sinking point of a mixture of 

 75 mutton (sinking point, 50-1) and 25 palm-oil (sinking 

 point, 39-2) :— 



75. 50-1 + 25. 39-2 



: = 47-37. 



75 + 25 



If butter be one constituent in the mixture, the formula 

 will be somewhat modified, inasmuch as butter contains, 

 besides fat, on an average, 15 per cent, of water, curd, and 

 salt, which, being removed by fusion, must not be admitted 

 into the calculation. 



One part of butter, therefore, is equal to 0-85 part of fat ; 

 the percentage of the butter present in the compound must 

 consequently' be multiplied by 0-85, to give per-cents of 

 butter-fat, thus : — 



0-85. B. 35-5 + F. S 



0.85 . B+F 



Example 2. — Calculate the sinking poiut of a mixture of 

 66-7 of butter and 33-3 tallow (No. 1 of our list of 

 mixtures) : — 



0-85. 66-7. 35-5 + 33-3. 53-3 



— — — ~=42-08 



0-85. 66-7 + 33-3 



The sinking point actually found, and that arrived at by 

 calculation, will not often coincide exactly, 85 per cent, 

 being taken as the -mean, and not as an absolutely constant 

 proportion of fat in butter. 



