161 
“The [iodine] numbers are quite constant if the iodine solution is pres- 
ent in sufficient excess; the excess, according to Ulzer, when the reaction 
eontinues for six hours, must be at least 50 per cent. of the iodine used. 
Fahrion uses an excess of 100 per cent. of the absorbed iodine (i. e., also 
50 per cent. of the iodine used) with a reaction of only two hours, and 
Holde recommends for this period of reaction the use of 75 per cent. ex- 
cess of iodine. * * * With a sufficient excess of iodine the results ob- 
tained are the same after two hours, six hours, and longer periods.” 
This refers to the use of the ordinary Hiibl’s solution of iodine and 
mereuric chloride, and in the experiments to be described the determina- 
tions were carried out in the usual way, varying the two factors—(1) 
excess of iodine, and (2) duration of reaction. 
Excess of Iodine.—It is stated in the passage above quoted that the 
iodine in excess must be at least 75 to 100 per cent. of the iodine absorbed, 
and that a larger excess will not affect the results if the reaction is not 
less than two to six hours in duration. 
To test this statement the writers made twenty determinations with a 
linseed oil, the mixture being allowed to stand six hours, and the excess 
of iodine ranging from .008 to 3.658 per unit of iodine absorbed. The ex- 
periments were made in three series, each series being carried out under 
as nearly as possible identical conditions, and in spite of two slight dis- 
erepancies in the twenty experiments, there was unmistakable evidence 
that the iodine number steadily and materially increased with the excess 
of iodine, the increase being nearly as marked between an excess of 1 and 
of 3.6 as below 1. The iodine numbers obtained varied from 131.2 to 175.3, 
those with an excess of over 1 from 161.9 to 175.3. 
Benedikt gives as minimum and maximum results for commercial lin- 
seed oil, according to twenty authorities, 148 and 181, with an average 
of 170. 
Duration of Reaction.—In the above citation from Benedikt, a duration 
of two hours is said to be sufficient if the excess of iodine is equal to 
that absorbed (Fahrion), or 0.75 times as great (Holde), while six hours is 
said to be enough for an excess of 1 according to Ulzer. 
The writers carried out eighty experiments to test this point, the ex- 
cess of iodine varying from .5 to 1.4, and the duration of the reaction from 
two to eight hours. The eighty experiments were made in six series, and 
only three of the eighty experiments failed to confirm the conclusion that 
11—Scrence. 
