aes - sci sriric RESEARCH. Ly odie ee pale 
a F pyridine and He ae may Ee titrated nea wht sitet ‘sation, with . sodium 
ret iromate ‘as indicator; since, furthermore, it had been found. that pyridine is able to 
| »sorb- quantitatively methy] iodide from strongly diluted gas mixtures, with formation — 
3 f the iodomethylate, a means was given hereby to abandon the silver solution when 
= stimating the methoxy! content of sulphuretted substances. 
= On these grounds, J. Th. Hewitt and W. J. popes?) suggested a modification of the 
usual ‘methoxyl estimation process. Ree ah 
_- The hydriodic acid was prepared by dota tee an aqueous suspension of iodine 
with hydrogen sulphide, distilling the resulting solution, and collecting the fraction 
3 boiling between 123 and 127° (d 1. 7). The pyridine need not be entirely freed from — 
-picoline; however, it is advisable to remove substances of high boiling point. 
_ The apparatus consists of the usual carbon dioxide generator, the decomposition 
flask heated in a glycerol ‘bath to 130°, and rectifying column (four-pear or other 
"suitable form). ‘The carbon dioxide carrying the methyl iodide vapour is passed through 
_ two test-tubes in series, each containing 10 cc. of pyridine. Removal of the excess of 
Pyridine before carrying out the titration is, according to the authors, unnecessary. 
For the estimation, a suitable weight of the substance is taken, 20 cc. of hydriodic 
“acid dd 1 0) are added, ‘and the heating maintained for one hour. The contents of the 
test-tubes. are conipletely washed into a graduated flask, when they are diluted with 
water. The iodine ion is titrated, after acidification with nitric acid, by adding a known 
amount of standard silver nitrate solution and titrating back the meray! of oe by 
Beseeyatiaie according to Volhard’s method. | 
In the course of the experiment, a coe Ealgatior develops in Othe pyridine. 
“This vanishes on dilution of the pyridine at the and of the experiment. It is not due 
to ) free iodine. Should, ‘however, the colour persist on dilution with vars it is then | 
advisable to discharge it with thiosulphate solution. | : 
; The analyses" pe soneiaied, inter aha: — 
i? peewee” Percentage of coed Gepoein 
Sgt Serie. eae found.) "calculated 
Methyl alcohol . 95.2 to 96.3 per cent. 96.9 per cent. 
_ Methyl salicylate 19. 7 per cent. | 20.4 per cent. 
Unsatisfactory results were obtained with methy! benzoate. 
In our opinion, it remains to be proved whether the method is suitable for estimating 
essential oils. a 
“Some years ago, C. A. Hill and T. T. Cocking?) deschbed a quantitative Me atiod for 
& timating cmnamic acid im storax which, briefly spoken, based on the fact that the 
saponified balsam was dissolved in water, extracted with ether, and acidulated; by 
T renewed extraction with ether the cinnamic acid is shaken out and estimated. This 
“ incitiod (now Official in the British Pharmacopceia, 1914) has been tried by Cocking and. 
Ke ttle *) for the estimation of the aromatic acids in balsam of tolu, but was abandoned, as . 
repeated extractions by boiling with water caused the resinous matter to become so stiff _ 
that it was impossible to extract the acids completely. It was found, however, that 
boiling out of the aromatic acids with magnesium oxide and water, in the presence of 
a small quantity of xylene to soften the resin, was the most Satisfactory way of dealing . 
wit! the balsam. The magnesium salts of the aromatic acids. are readily soluble in cold 
wa at er those :of the resin acids being insoluble. 3 
———— / 
F =) Tourn. chem. Soc. 115 (1919), 193. — 2) Chemist and Druggist 80 (1912), 412; Report October 1912, 126. 
y Americ. Bayer Pharm. 9 ae 119. | ‘ 
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