MKTIIODS OK ANALYSIS. 



17 



From these ivsult> it is smi that the correction of the index of 

 refraction for 1 ( J, U practically a constant I'nr all of the oils examined, 

 while the correction in scale divisions varies from O.T>5 to ().:'> for 

 1 C. For givat changes of temperature it is not accurate to u-c the 

 scale division factor, hut the results must he reduced to indice- of 

 refraction and the correction applied to them. The following formula 

 may lie used to correct for a range of 10 degree.-: 



R =R' + X(T'-T). 



R = reading convctol t<> T. 



R' = reading at, T'. 



T =di'snv<l temperature. 



T' = temperature nt \vliieh readings arc made. 



X == change in scale division caused by a change of temperatore of ] < '. X 0.56 



for butters; 0.:>S f,, r oils that read from 60 to 70 on the scale; ami (Ui'J for 

 oils that iva.l from 70 to SO .) 



The determination of the index of refraction has much the sime 

 value in the detection of adulteration as the determination of specific 

 gravity. The forty -two samples of California oils examined had a 

 range of from 1.4703 to 1.4718, with an average of 1.4711. These 

 limits exclude one sample having 44 per centof free acid and an index 

 of 1.4HL\ as free acid reduces the index of refraction of an oil. 

 Blasdale a on eleven samples of California oils obtained a range of 

 1.4710 to 1.4716. Colby 6 gives a range for California oils of fron: 

 L4()S9 to 1.4717, but this is probably too wide for oils which can be 

 cla-sed as salad oils. On eighteen samples of pure Italian oils reported 

 in this bulletin there was found a range of from 1.4703 to 1.4713. 

 There is therefore a total variation in the determinations made in 

 this laboratory of from 1.4703 to 1.4713, with no difference between 

 the California and Italian oils. Table VIII gives the index of refrac- 

 tion obtained on various oils. 



TABLE VIII. Butyro-refrcictorneter ri<i(lii></x <m<l /v;/Vm7//r iinl!rcx ofol/x. 



Jour. Amer. Chem. Soc., 1895, 17: 935. 

 ''('iiliforniji Agri. Expt. Stu. Kept., ls7-js, p. 169. 



'One sample of ju-annt oil containing l.'i.Sl per cent of free acids hacl an inl-\ .if 

 refraction of 1.4707. 



201 28 X o . 77- -05 3 



