252 DECALCIFICATION, DESILICIFICATION, ETC. 



dilute, but causes serious swelling of the tissues. To remedy this, 

 chromic acid or alcohol may be added to it. Or a 3 per cent, 

 solution of the acid may be taken and have dissolved in it 10 to 

 15 per cent, of common salt. Or (WALDEYER) to a T Q\JO per cent, 

 solution of chloride of palladium may be added T \y of its volume of 

 HC1. 



Chromic acid is also much used, but has a very weak decalcifying 

 action and a strong shrinking action on tissues. For this reason 

 it should never be used in solutions of more than 1 per cent, strength, 

 and for delicate structures much lower strengths must be taken. 



Phosphoric acid has been recommended for young bones. 



Acetic, lactic and pyroligneous acids have considerable decalci- 

 fying power, but cause great swelling. Picric acid has a very slow 

 action,, and is only suitable for very small structures. 



548. Nitric Acid (Buscn, loc. cit.). To all other agents BUSCH 

 prefers nitric acid, which causes no swelling and acts most effica- 

 ciously. 



One volume of chemically pure nitric acid of sp. gr. 1-25 is diluted 

 with 10 volumes water. It may be used of this strength for very 

 large and tough bones ; for young bones it may be diluted down 

 to 1 per cent. 



Fresh bones are first laid for three days in 95 per cent, alcohol ; 

 they are then placed in the nitric acid, which is changed daily, for 

 eight or ten days. They must be removed as soon as the decalcifica- 

 tion is complete, or else they will become stained yellow. When 

 removed they are washed for one or two hours in running water and 

 placed in 95 per cent, alcohol. This is changed after a few days for 

 fresh alcohol. 



Young and foetal bones may be placed in the first instance in a 

 mixture containing 1 per cent, bichromate of potash and ^ per 

 cent, chromic acid, and decalcified with nitric acid of 1 to 2 per 

 cent., to which may be added a small quantity of chromic acid 

 (T^ P er cen "t.) or bichromate of potash (1 per cent.). By putting them 

 afterwards into alcohol a green stain is obtained. 



549. Nitric Acid (^CHAFFER, Zeit. wiss. Mik., xix, 1903, p. 460). 

 SCHAFFER also finds nitric acid the best reagent. It should be taken 

 pure ; the addition of formol, alcohol, or the like, slows the reaction. 

 The best strength is from 3 to 5 per cent. Objects must not be 

 washed out directly with water, and washing in salt solution, alcohol, 

 phloroglucin, or formol is not sufficient to prevent swelling. Alum 

 in 5 per cent, solution is good, but not necessary. Material should 



