Notes on scientific research. , 91 



We should particularly point to the behaviour of clove oil and of eugenol. Although 

 the clove oil used contained 82 per cent, of eugenol, the solubility of these two pro- 

 ducts was strikingly different (compare table below). The case exemplifed how much 

 very slight variations in the composition of essential oils can influence their properties. 

 The table is a summary of the results of Wood's experiments: — 



Solubility in 100 parts of alcohol at different concentrations 



Per cent. ^ 



alcohol " Oil of anise Cinnamon Cloves Eugenol Peppermint Sassafras 



30 p.c 0.05 0.02 0.02 0.07 



40 p. c 0.08 0.10 0.30 0.02 0.10 



50 p.c 0.10 0.20 0.40 5.80 0.03 0.20 



60 p.c 0.25 0.40 2.00 16.00 0.06 1.30 



65 p.c 0.80 1.10 10.00 . 0.07 • 2.3 



70 p.c 1.50 2.20 21.75 — 0.10 4.00 



75 p.c 4.00 7.00 — 0.17 7.00 



80 p.c 7.50 — — — 0.35 11.00 



In an extensive paper F. Eisenlohr and E. Wohlisch 1 ) show with reference to some 

 400 compounds, taken from the literature, that the molecular coefficient of refraction, 

 that is, the product of refractive index and molecular weight, represents a valuable 

 supplement to the molecular refraction and dispersion, particularly in researches on 

 the constitution. From the normal series of the paraffins, primary alcohols, aldehydes, 

 ketones, acids and esters he deduced the mean fundamental value of the molecular 

 index of refraction MXn D20 o for the methylenic group, the constant CH 2 = 20.56. The 

 influence of the ethylene-bond [/ = = — 6.7], and of hydrogen [H = — 4.99] appeared 

 as a negative quantity (decrement). The highest value would then be attached to 

 oxygen in its saturated bonding, the hydroxyl oxygen [O* = 26.54], the lowest value 

 to the double-bonded carbonyl oxygen [O" (in ketones) = 16.98]. The limit of error 

 for the expression M X n D20 o is 0.2 unit. Eisenlohr considers that the molecular 

 coefficient of refraction furnishes a simple and reliable means of testing a liquid 

 compound for its purity. 



The study of the influences which the constitution of the compounds has upon the 

 product M X n D20 o led to the following general results: — In acyclic compounds the entry 

 of a side-chain into a position next to the carbon atom at the end of a chain decreased 

 the value of the molecular coefficient of refraction by 0.2 unit with respect to the 

 value calculated from the equivalent. On the other hand, the entry of a side-chain 

 into a position further removed from the extreme carbon atom raised its value by 

 0.45 unit. In cyclic, non-aromatic bodies distinct influences were noticed of the 

 different cyclical linking, the decrements increasing steadily from the 8-member-ring 

 to the 3-member-ring. The entry of a side-chain caused, by contrast to the acyclic 

 compounds, a further diminution of the value M X n D20 o (increase of the depression). 

 Homologues differed from one another according to the mutual position of the side- 

 chain and the double linking. 



The aliphatic acids and esters occupied in so far a special position, as the observed 

 values for the molecular coefficient of refraction were found to be lower by 2.23 to 

 2.65 units than the calculated values. Since now the ring-formation always introduced 

 a specific decrement, the authors assume that acids, like esters, form a kind of ring 

 owing to some accessory binding. 



>> Berl. Beriehte 53 (1920), 1746. 



