26 U. S. BUREAU OF FISHERIES 



glass or rubber stoppers. It contains some colloidal matter, pre- 

 sumably protem, and is therefore incompatible with protein coagu- 

 lants, alcohol, heat, etc. Gelatin, fish glue, isinglass, etc., may be 

 dissolved in it directly. Another preservative for the aqueous sus- 

 pension is 0.3 per cent salicylic acid dissolved in the water. If 

 traces of iron are present (as they often are) the suspension will be 

 pinkish. 



NONAQUEOUS SUSPENSIONS AND LACQUERS 



Pearl essence may be found on the market in the form of suspen- 

 sions in acetone and amyl acetate. It is also sold in the form of a 

 thick paste as crystals suspended in a viscous lacquer of celluloid in 

 amyl acetate. Other liquid vehicles may be used. The writer has 

 made suspensions in ethyl acetate (which evaporates more rapidly 

 than amyl acetate), acetic aldehyde, glacial acetic acid,- acetic 

 anhydride, chloroform, carbon tetrachlorides, etc. 



Methods of manufacture of these preparations are mostly trade 

 secrets, and some steps in them are covered by patents.^ One such 

 patent (Paisseau, No. 978394) covers the progressive dehydration 

 of the aqueous suspension by replacement with a nonaqueous liquid 

 that is miscible in all proportions with water, such as alcohol or 

 acetone, or in limited proportions, such as ether. The same patent 

 also claims the transfer of the particles to amyl acetate by addition 

 of the latter liquid to the aqueous suspension and boiling off the 

 water, which has a lower boiling point than that of amyl acetate. 

 Once the particles are in amyl acetate, they may be concentrated 

 by sedimentation or centrifugation and celluloid added to produce 

 the viscous paste preparation. One such preparation examined by 

 the writer contained about 13.5 per cent each, by weight, of cellu- 

 loid and guanin particles, and 73 per cent amyl acetate. Pearl 

 essence suspensions intended to be used for celluloid lacquers or 

 celluloid plastics should be free from all traces of ammonia, which, 

 if present, will cause the celluloid to turn yellow. 



A method of preparing pearl essence in nonaqueous suspension, 

 devised by the author of this paper, depends on the property of 

 guanin particles of being wetted by certain liquids, like ether, more 

 readily than by water. If ether is emulsified mth a suspension of 

 pure guanin particles in water, and the two liquids are allowed to 

 separate, the guanin particles will be found in the ether layer above 

 the water. Other matter present will remain in the water layer. Not 

 only ether, but other liquids of the fat-solvent class, such as chloro- 

 form, benzol, carbon tetrachloride, toluene, etc., have this same 

 property of driving water from the surfaces of the crystals, thus sepa- 

 rating them by a kind of flotation from the impurities with which 

 they are associated in the crude washings from the scales. 



The principle involved in this flotation is an interesting and im- 

 portant one in both physical and industrial chemistry. Metallic 



• J. Paisseau. Composition for use in the manufacture of artificial pearls. United States patent No. 

 978394, Dec. 13, 1910. 



J. Paisseau. Manufacturing of artificial pearls and other nacreous objects. United States patent No. 

 1438395. 



Q. Keil and K. Plischke. Verfahren zur Herstellung von Silbcrtinktur. German patent No. 215672, 

 Oct. 30. 1909. 



Q. Leroy and Cie. Perfectionnement & la fabrication des perles fausses. French patenttNo.t473662,[Oct. 

 8, 1914; also additions Nos. 19477, 19522, and 20258. 



For a list of German patents see Von Unruh, 1918. 



