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ANIMAL PROTEINS 



2. The proportion of hypo is increased somewhat for 

 the heavier classes of goods, and may even reach 20 per 

 cent, of the pelt weight. 



3. An increase in the proportion of hypo is usual with 

 an increase in the amount of free acid in an acid chroming 

 bath. 



4. The percentage of hydrochloric acid in the reducing 

 bath is roughly half that of the hypo, but is the most 

 variable factor. The quantity varies with the rate and 

 mode of addition, the class of goods under treatment, 

 and the composition of the chroming bath. 



5. In baths of the Schultz and neutral type it is better 

 to add some acid to the hypo bath before adding the goods, 

 but this is less essential for goods from an acid chroming 

 bath. 



6. In the case of goods from acid chroming baths, 

 the amount of acid used in the reducing bath is an inverse 

 function of the excess of acid in the first bath, e.g. take 

 the following two processes : 



7. There should be some excess of hypo at the end of 

 the process. This acts as a feeble alkali, and commences 

 the neutralization. 



The process can be carried out in paddles or in drums 

 as preferred, for reasons similar to those applicable in the 

 case of the first bath. On the whole, however, drums are 

 less popular for the second bath, for the dilute solutions 

 of the paddle effect some economy of sulphurous acid, 

 which is apt to escape into the air. A preliminary " hypo 

 dip " is sometimes used to prevent the " bleeding " of 

 the chromic acid. The use of many other reducing agents 



