27 



applied at once. Their efficacy increases in a geo- 

 metrical progression. 



" When the several infusions yielded by one sam- 

 ple are united, the average liquor will in general 

 be found sufficiently weak to be acted on by skin 

 with the greatest effect ; that is, to afford all the 

 colouring matter along with the tan — an advantage 

 the tanner is prevented from obtaining in strong 

 decoctions of bark. If his experience should lead 

 him to think a particular infusion too strong (which 

 may occur in the examination of astringent extracts 

 similar to kino, rhatany, and catechu,) he may add 

 water to reduce it to what he would call a " safe 

 tanning strength." Aliquot parts of these infu- 

 sions (one-sixth of each for instance,) are now to 

 be separately submitted to the action of the test 

 skins (to be described afterwards) which should be 

 carefully handled in the liquors now and then for 

 seven or eight hours, to expose new surfaces to the 

 action of the ouze, till the tanner ascertain, by eye 

 and tongue, that the liquors are absolutely spent. 



There are a number of critical appearances in 

 various operations, altogether undescribable, and 

 of which inanimate tests give us no warning, and 

 keep no record : In such cases it fortunately hap- 

 pens that the organs of sense give perfect satisfac- 

 tion to an experienced operator. In the process 

 under consideration, habit renders their decision 

 all-sufficient. 



The skins intended for the trial should previous- 

 ly be well washed in tepid water, to extract any 

 lime which they may have absorbed in the process 

 of depilatiou, together with all the loose gelatine 



