( 339 ) 



their deusity, refructive power and meltingpoiiit. Ut' tliese eight, three 

 were entirely unknown viz caproin, caprylin and caprin ; three: buty- 

 rin, pahnitin and stearin had formerly been prepared synthetically, 

 but the former two certainly not pure ; two : laurin and myristin had 

 only been obtained from natural products, but neither quite pure. 



The method of preparation adopted by Mr. Sciiey consists simply 

 in heating glycerin with an excess of the acid up to a temperature 

 at which neither the glycerine, nor the acid, nor the ethereal salt 

 suffer decomposition and under circumstances in which the water 

 formed is immediately drawn off as completely as possibly e.g. by a 

 slight current of air and under diminished pressure in the apparatus, 

 this being followed by fractional distillation in vacuo or crystalli- 

 zation from diiferent solvents, until one of the properties mentioned 

 underwent no further noticeable alteration by this treatment. This 

 fact led to the conclusion of the purity of the product; Mr. Schey 

 attaching little value to elementary analyses in these cases, they 

 have not been made. 



The determination of the specific gravity was always done by 

 weighing a certain volume of the substance and an equal volume of 

 water at the same temperature; the exactness acquired in this way 

 holds good up to one or two unities of the 4"^ decimal. 



The refraction-index was determined for sodium light with a refrac- 

 tometer of Pulfrich with which generally the 4"' decimal is certain. 

 The determination of the meltingpoint has not been so exact, but 

 that differences of one or two tenths degrees may occur. 



Mr. ÖCI1EY has not only determined the three properties of his 

 products, but also of the original substances (the acids), which were 

 purified to the highest possible degree, except the two highest acids, 

 which Dr. L. E. 0. de Vissee of Schiedam had kindly procured 

 him in a veiy pure condition. Of the eight triacylins prepared, 

 tricaprin offers the highest guarantee of purity because it crystallizes 

 best of all and was obtained in great, clear, well-formed crystals ; the 

 lower terms are at the ordinary temperature liquids of whicli tribu- 

 tyrin alone has an intensely bitter taste. 



Finally Mr. Schey treats of the methods by which it is possible 

 to calculate, approximatively at least, density and refractive power 

 of these substances. The calculation with the numbers determined by 

 others for the atomicvolumes (even Trauce's with the co-volumes) 

 and for the atomicrefractions, gives results differing pretty much from 

 those found by liim. He here points out the little certainty offered 

 by the generally accepted values for atomicvolumes and atomic- 

 refraction. 



23* 



