138 



Mr. E. Schunck on a Crystalline 



[Recess, 



colourless. After being washed it is dissolved in alcohol. On spontaneous 

 evaporation the solution leaves a perfectly white crystalline residue con- 

 sisting of the acid in a state of purity. 



As thus prepared, the substance has all the properties characteristic of 

 the group of fatty acids to which palmitic and stearic acid belong. It is 

 white, has a pearly lustre and a crystalline appearance, and when viewed 

 under the microscope is seen to consist of small star-shaped masses. From 

 a solution in boiling dilute spirits it is deposited, on the solution cooling, in 

 shining scales. The alcoholic solution reddens litm.us-paper slightly ; it 

 floats on the surface of water, which it repels like all other fats. "When 

 the water is heated, it melts into oily drops, which on cooling become solid 

 and crystalline. Its melting-point, as determined with an apparently pure 

 specimen, is 54°'3 C. When impure, i. e. contaminated with the body 

 which imparts the brownish-yellow colour to the crude product, it fuses at 

 a lower temperature. A specimen only slightly coloured melted at 52°*8 C, 

 another at 49°' 5 C. -When heated between two watch-glasses, the acid 

 fuses and is then volatilized, leaving only a trace of residue, while there is 

 formed on the upper glass an oily sublimate, which on cooling becomes 

 solid and glassy. This sublimate dissolves easily in alcohol, and the solu- 

 tion leaves on spontaneous evaporation a white crystalline residue consist- 

 ing of needles arranged in star-shaped or feather-like masses. The sub- 

 stance dissolves as easily in ether as in alcohol, and the solution leaves on 

 evaporation a white crystalline mass. It is easily soluble in boiling dilute 

 caustic potash and soda-lye, as well as in aqueous ammonia ; these solu- 

 tions froth on being boiled like those of ordinary soap. The solution in 

 potash deposits on cooling a quantity of white pearly scales, which settle 

 slowly to the bottom of the vessel. The soda compound separates in the 

 form of a thick, white, amorphous soap, a very small quantity of which is 

 sufficient to cause the liquid to gelatinize on cooling. The ammoniacal 

 solution deposits on cooling a quantity of scales, which resemble the 

 potash compound, together with a few crystalline needles. Boiling solu- 

 tions of carbonate of potash and carbonate of soda also dissolve the acid 

 readily. "When the residue left by evaporating the solution in carbonate 

 of potash to dryness is treated with boiling absolute alcohol, an alcoholic 

 solution of the potash-soap is obtained, which, after being filtered from 

 the excess of carbonate of potash and spontaneously evaporated, leaves a 

 residue consisting partly of isolated prismatic crystals, partly of star-shaped 

 masses. The soda compound may in the same manner be obtained in a 

 crystalline state. The alcoholic solution of either of these compounds gives 

 with acetate of baryta a white crystalline deposit. A watery solution gives 

 with nitrate of silver a white, curd-like precipitate, which blackens slowly 

 on exposure to the light. The ammoniacal solution of the acid produces, 

 with the chlorides of barium raid calcium, white, flocculent precipitates, 

 which do not become crystaUine on standing. The alcoholic solution yields 

 with acetate of lead, an abundant white amorphous precipitate. 



