APPENDIX. 153 



Page 55, 3. I would suggest temperature of water bath, say about 100 instead of 

 110 C. A great many laboratories! have only water baths, and the temperature 

 obtainable is only 100 C. -/. A. Le Clerc. 



Comment. />>/ Mr. ]\'inlnn. Temperature of 110, although in some ways not so con- 

 venient as 100, facilitates the removal of the volatile oils. 



1 'age 56, 10. Most published methods involve the assumption that oil of cloves 

 exerts no vapor pressure at ordinary temperatures. This is very far from being the 

 ease. In the process described on page 2, a mixture of ether and oil of cloves will 

 lose both ether and oil of cloves when allowed to "evaporate at room temperature." 

 A second loss will take place in standing eighteen hours over sulphuric acid, the 

 sulphuric acid continually absorbing the vapor of the oil as it is given off. 



If cloves are finely powdered and exposed to the air in a thin layer, it will be found 

 that after the lapse of a week or two the loss in weight which has taken place will be 

 approximately equal to the amount of volatile oil originally present. The final 

 weight, or rather the weight after the oil has evaporated, will vary slightly with the 

 pressure of water vapor in the atmosphere. The fact that commercial ground cloves 

 often contain very little volatile oil may sometimes be due to the fact that the cloves 

 have been long ground, the oil having escaped by evaporation. 



The correct method indicated would seem to be: 



(1) Allow one of the volatile constituents to become in equilibrium with a limited 

 atmosphere kept continually saturated with this constituent (e. g., water) at a given 

 ten i]>erature. 



(2) Allow the other volatile constituent (oil) to evaporate completely into an 

 unlimited atmosphere free from this constituent. 



(3) Restore the original conditions in (1). 



The difference in weight between (1) and (3) w r ill give the weight of the second 

 constituent. 



(All the oil and water may be driven off by a few hours' heating in a \vater oven.) 

 I have used various modifications of the above principle, but have so far had no 

 opportunity of checking their absolute accuracy, as all published methods seem to me 

 wron<; in principle for the reason already given. E. B. Kenrick. 



Page 56, 10. A student in this laboratory, Mr. L. L. Watters, last year made some 

 experiments in regard to the determination of oil of sage by a method practically 

 the same as this, except that very light petroleum ether was used for extraction. He 

 found that it was difficult to drive off all of the ether without some of the oil, or to 

 tell when all the solvent was driven off. Also sage oil left a residue, small, but 

 rat her variable, when evaporated, ami brought to constant weight at 100 C. He 

 thought the amount of residue thus left was influenced by the other constituents of 

 the ether extract. A partial correction was obtained by adding to an aliquot part of 

 the ether solution, before evaporation, a known weight of sage oil and carrying this 

 through the same process as a blank. Possibly it might be worth w r hile to try some- 

 thing of this sort with other volatile oils.//. C. Sherman. 



Com UK' nt l>i/ M,-. ]Vinton. Our standards are based on ether extraction. The 

 method, we know, is not perfect, but we should go slow in making changes. The 

 points named are worthy of further study. 



Page ")(;, 10. Could not petroleum ether or gasoline be used alternatively here or 

 wherever extraction with absolute ether is recommended? The latter is better on 

 account of the dilliculty of keeping the ether perfectly anhydrous during the extrac- 

 tion. -A. (!. }\'<x>(liixiii. 



Comment />>/ Mr. Wmton. Petroleum ether has certain advantages over ether, but 

 among the disadvantages in this instance is the fact that our standards of composition 

 are based on the other method. 



