BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 103 
It will be noticed that in all cases an increment of CHo brings about an increase in 
the temperature of .equal slope, and in all cases the increase becomes greater as the 
series is ascended. In any group of normal isomers the formate has the largest 
temperature value and, with the possible exception of ethyl propionate, the remaining 
esters in the group have almost the same value. According to the general rule, 
methyl isobutyrate has a lower value than methyl butyrate, and, as in the case of the 
ketones, of the two ethers, diethyl and methyl propyl, the symmetrical isomer has 
the lower equal-slope temperature. 
Appendix. 
On the Preparation of Ethers. By R. E, Barnett, B.Sc., Assoc. P.C.S. 
The ethers prepared and used for viscosity observations were methyl propyl, ethyl 
propyl, dipropyl, methyl isobutyl, and ethyl isobutyl. 
The most rapid and economical method of preparing certain ethers is undoubtedly 
the “ continuous etherification ” of alcohols by means of sulphuric acid, first used by 
Boullay and investigated by Williamson. Although it has been shown, originally 
by Williamson (‘Annalen,’ 81, 77) and later by Norton and Prescott (‘Amer. 
Chem. Journ.,’ 6, 241), that this method is applicable to the preparation of mixed 
ethers, there are always formed, as would be expected, considerable quantities of the 
two possible simple ethers containing the same alkyl radicles. The great difficulty of 
separating any one ether from such a mixture, and the absence of any certain chemical 
method of ascertaining the presence of isomers, render this method particularly unsuit¬ 
able for preparing ethers for physical investigation. The liability of the higher fatty^ 
alcohols to oxidation by the sulphuric acid, which limits the application of this method 
to alcohols containing not more than three carbon atoms (Norton and Prescott, Ioc. 
cit.), is partially obviated by the employment of the sulphonic acids of benzene, 
naphthalene, and similar compounds (Krafft, ‘ Berichte,’ 26, 2829). 
Although it is evident that the d irriori objections mentioned above apply equally 
to this method, it was tried in preparing dipropyl ether. Employing benzene- 
sulphonic acid, :i liberal supply of which we ovve to the kindness of Messrs. Brooke, 
Simpson, and Spiller, considerable difficulty was found in getting anything like 
complete etherification. Much propyl alcohol always came over with the ether, and 
as their boiling-points only differ by some seven degrees, the mixture was difficult to 
separate by fractionation. A better residt was obtained by passing the first product 
through the acid again, but still much alcohol was present. After a rough separation, 
the ether was repeatedly treated with sodium wire, until further action practically 
ceased. The I’esulting product was fractionated four times in a Lebel-Henninger 
apparatus. It was evidently^ a mixture, containing presumaldy also di-isopropyl and 
