94 THE SCIENTIFIC ASPECTS OF TANNING. 



considerable accuracy. This subject was brought before the 

 British Association at Aberdeen, 1859, in a paper read by- 

 Messrs. Mulligan and Dowling, students at the Museum of Irish 

 Industry, under the direction of Professor Galloway, who very 

 kindly gave us particulars as to the apparatus employed. One 

 hundred grains are allowed to soak for some hours in cold water, 

 then placed in this long tube 3 the cold water gradually passing 

 through the bark carries down with it, all the Tannic Acid, into 

 the bottle below. In our .^quotations of the value of different 

 tanning agents, we have given the percentages as placed before us 

 in their paper as being most reliable, great care having been taken 

 to insure accuracy in the analyses. 



But, two things interfere with gelatine analysis. First, it is at 

 times very doubtful when the exact point of saturation is reached 3 

 and also with some materials, such as Gambice, D. Divi, the use of 

 gelatine is impracticable. With Gambice, the reaction is very 

 feeble 3 and with D. Divi the solution rapidly assumes the condition 

 of thick milk 3 and It is impossible to get at any accurate result. 



Acetate of lead and copper have been employed volumetically, 

 and by weight of precipitates 3 but as both of these will precipitate 

 any other organic acids which may be in the solution, such as 

 gallic acid, they have often given false results. Lowenthal's 

 method, which is much commended by chemical works, is a very 

 beautiful experiment, fit for the table of the lecture room. But 

 the presence of other organic matter, with the very minute 

 quantities which can be tested have proved an obstacle in its 

 general use. 



Mr. Stoddart speaks very favorably of acetate of lead employed 

 in conjunction with ferri-cyanide of potassium as an indicator, 

 the exact point of saturation being shown by a red tinge becoming 

 permanent in the solution. We have as yet given but little 

 attention to this reaction, but imagine it to be the most satisfactory 

 method of testing for tannic acid. It only remains for us to 

 speak of the new apparatus, which is the joint invention of two 

 Frenchmen, Messrs. Muntz and Ramspacker, one of whom has 



