176 



avoid as much as possible the danger of allowing your limes to be- 

 come too much saturated with nitrogenized matter; use only enough 

 for the time; sulphur will always assist the lime. I would have made 

 several experiments, only that I had not the apparatus. I propose 

 the use of an apparatus for liming, such an one as I have had in pri- 

 vate use for some time past. 



DRENCHES. 



The exuvia of fowls and reptiles yields upon exposure to a humid 

 atmosphere oxylate of ammonia; in water, with considerable agita- 

 tion, carbonate of ammonia; thus you perceive the intuitive process 

 of agitating the drenches from time to time. The ammonia is taken 

 up by the hide whilst the carbon is combined with the lime, forming 

 carbonate of lime, or chalk, which is very injurious to the hide, and 

 when in excess prevents the necessary reduction. The test for the 

 presence of chalk is to take up in a glas.s some of the suspected im- 

 pure drench and drop into it a few drops of acetic acid. Efferves- 

 cence or foaming will indicate the presence of chalk. In large 

 tanneries a quantity of air may be blown into the drench until the 

 lime is precipitated, when the supernatant liquor of ammonia rnay be 

 drawn off and used again with a small addition of excrement. 



I have found that weak liquors, rich in acid produced by mucilagi- 

 nous ferment are of great use in reducing the skin and expelling the 

 lime. Baths of sulphurous acid are also as good (if properly man- 

 aged) as drenches made from exuvia, especially if uric acid in proper 

 proportions be held in intimate solution with the acid. 



SWEATING PROCESS. 



1 



Sweat-houses are made, as you all know, by building a place almost 

 air-tight, through which water or steam is caused to pass. H. is 

 evolved, affinity for N. ie*disengaged and ammonia is formed, first 

 from water vapor; 2 vols. H., 1 vol. O- form 2 vols. aqueous vapor, 

 and 3 vols. of A. V. 1 of N. form ammouiacal gas, and ammonia 

 has a great affinity for sulphur, and the greatest quantity of sulphur is 

 found in the mucous canal of the skin, consequently the roots of the 

 hair are decomposed by the caustic action of ammonia, and thus dep- 

 ilation is secured. This method is not to be recommended for upper 

 leather, as the fatty portion of the hide is not by this means sufficiently 

 decomposed, and to use acids strong enough for the purpose would 

 injure the texture of the skin, it being too thin. I have seen a few 

 days since, in the tannery of Mr. Rawlston of Bertheu, a compound 

 process. The lime-house is part a sweat-room ; he uses sulphur in 

 the limes; the hides are exposed to the action of the ammoniacal gas 

 as well as the action of lime, and are limed very low. They use no 



