KESULTS OF ANALYSIS. 19 



The leathers here analyzed were secured from various sources ; some 

 were sent by tanners, some by shoemakers, some by sole cutters, 

 and others were purchased from dealers. In some cases it was 

 impossible to learn who tanned the leather; in the other cases the 

 name of the tanner was given by the dealer, or his trade-mark or 

 name appeared on the leather. Beyond this nothing is known as 

 to the source of the leathers. 



In the third column the approximate date of receipt of the leather 

 is indicated. It will be observed that many of these samples are 

 5 or 6 years old. Comparison with samples taken more recently 

 does not indicate material change in tannery practice with respect 

 to loading. 



Referring to the tables, the " Moisture" consists of the water 

 which the leather exposed to the air naturally contains in addition 

 to all the water of crystallization of any Glauber's salts, or sodium 

 sulphate, and five-sevenths of the water of crystallization of any 

 Epsom salts, or magnesium sulphate, which may be in the leather. 

 . In the column headed "Ash" are given the residues from burning 

 the leather. These residues include the ignited, dehydrated soluble 

 salts which may have been in the leather, such as Epsom and Glau- 

 ber's salts. 



Parker * has shown in an extended investigation that the insoluble 

 ash of sole and harness leathers, even though they be heavily weighted 

 with soluble salts, averages less than 0.2 per cent, and very rarely 

 exceeds 0.3 per cent. As none of these leathers was. weighted with 

 insoluble minerals, in those cases where the ash exceeds 0.3 per cent 

 such excess is included as part of the total water-soluble material 

 and so treated in calculating the combined tannin. 



The column headed " Petroleum ether extract" shows the percent- 

 age of fats and greases which the various leathers contain. 



The " Water soluble material" embraces soluble tannins and non- 

 tannins. The latter include glucose, Epsom salts (minus five- 

 sevenths of its water of crystallization, which is included under mois- 

 ture), and practically all but about 0.3 per cent of the ash. The sum 

 of the moisture, insoluble ash (assumed here to be 0.3 per cent), 

 total water soluble, and the hide substance (calculated from the deter- 

 mination of nitrogen) subtracted from 100 approximately equals the 

 combined tannin, which is combined with hide to form leather. 



The figures for Epsom salts show the amount of this salt (MgSO 4 -f 

 7H 2 O) present in the air-dried leathers. The column headed " Glu- 

 cose" shows the amounts of water-free glucose and dextrin which the 

 leathers contained, calculated as dextrose. In the last column is 

 given the ratio of combined tannin to hide; that is, the number of 

 parts of tannin combined with 1 part of hide to form leather substance. 



J. Soc. Chem. Ind., 1910, t9: 315. 



