( 396 ) 
That 109°.15 is the solidifying point of pure aceto-o-toluidide was 
proved by reerystallising the oxalate prepared from a “chemically 
pure” o-toluidine and then recovering the toluidine, which was then 
treated once more in the same way. 
After each crystallisation of the oxalate a small quantity of o-tolui- 
dine was converted into the acetocompound; the observed solidifying 
points were both the above figure, which moreover did not suffer 
any change when the acetocompound was again recrystallised. 
In order to ascertain how far small quantities of para-toluidine 
and aniline may de detected by means of the solidifying point tigures, 
the above purified o-toluidine was mixed with 2°/, of aniline and 
another portion with 2°/, of p-toluidine and tested as follows: 
25.2 grams of oxalic acid (*/; mol.) are dissolved in a litre of 
boiling water and to this are slowly added 42.8 gram of toluidine 
(?/, mol.). On cooling, the oxalate crystallises out; after placing the 
flask in ice the liquid is thoroughly removed by suction and the 
crystals washed once with a little water; the toluidine is then 
recovered from the crystals as well as from the motherliquor by 
adding alkali and distilling in a current of steam. In order to avoid 
loss it is necessary to extract the water, which has also distilled 
over, twice with ether. The toluidine so obtained is converted into 
the acetocompound by adding per gram a mixture of 2 cc. of glacial 
acetic acid and 1 ce. of acetic anhydride. The mass is now evaporated 
on the waterbath and the dry residue once distilled in vacwo when 
everything passes over leaving but a small black residue. The solidi- 
fying point of both products is then determined. We found : 
Added 
2/, p-toluidine 2°/) aniline 
Solidifying point of the acetotoluidide from the crystals : 109.715; 109.215 
5 EN Hs 3 > » motherliquors: 103.°2 ; 103.°0 
This shows that while the oxalate erystallised out, the added 
impurities remained completely in the motherliquor and that the 
acetocompound prepared from the latter shows the serious depression 
of about 6°. If now we consider that the determination of the 
solidifying point is accurate to 0.°2 and with practice even to 0.°1 
it follows that we may detect in this way '/,, part of the impurities 
now present, viz. */,, or 0.03 °/,. 
Using this method I have examined two samples of o-toluidine 
from different makers and both marked “chemisch rein” as to their 
purity with the following result. 
I. Converted into oxalate in exactly the same manner as described. Flask cooled 
in ice water. 
