82 



paper should be omitted, as the determination can be made more conveniently on a 

 gooch crucible as ordinarily used. 



Attention is also called to the accompanying paper involving some of Mr. \V. C. 

 Taylor's work on caffetannic acid and caffein. 



ESTIMATION OF CAFFETANNIC ACID AND CAFFEIN IN COFFEE. 

 By A. G. WOODMAN and W. C. TAYLOR. 



In connection with an examination of the methods for coffee analysis the writers 

 have made a study, in the limited time available, of the provisional methods for 

 determining caffetannic acid and caffein, especially the former. 



CAFFETANNIC ACID. 



Experience has shown that with the directions as given at present it is practically 

 impossible to obtain concordant results or a lead caffetannate of constant composition- 



It has been the general experience of those who have worked with the Krug method 

 that it is tedious in the extreme, and, furthermore, that the composition of the so-called 

 lead caffetannate obtained varies with the conditions of precipitation. It was our 

 purpose to ascertain if possible the source of some of these difficulties. 



It was seen early in the work that variations in the amount of lead acetate used 

 for precipitation gave variations in the proportion of lead caffetannate obtained, as 

 well as in its content of lead. This is shown in the following table, in which the 

 determinations were made on aliquot portions of a coffee infusion and varying amounts 

 of saturated lead acetate were used, all other conditions being kept constant. 



Determination of caffetannic acid, using varying amounts of lead acetate. 



The averages of several results are stated in each case, although the results showed 

 very considerable variation. While too much reliance can not be placed on these 

 figures, owing to variations among themselves, they show the necessity of using a 

 definite amount of lead acetate for the precipitation. 



Another source of error is the difficulty of washing the lead caffetannate free from 

 lead acetate. Those who have attempted it know the tediousness and the difficulty 

 of washing the precipitate on the filter. It is of course necessary to use alcohol of 90 

 per cent strength in washing, on account of the solubility of the precipitate in water 

 or dilute alcohol. On the other hand, the lead acetate which is to be removed is only 

 slightly soluble in 90 per cent alcohol. Hence it will be readily seen that it is practi- 

 cally impossible to wash the bulky precipitate on the filter. It is true, also, that when 

 the wash water no longer reacts for lead the precipitate is not necessarily free from it, 

 since owing to its character the wash water easily forms channels and does not wash it 

 thoroughly. 



After numerous experiments, washing by the centrifugal machine was tried, giving 

 several treatments with 90 per cent alcohol in the tubes of the centrifugal before trans- 



