298 



atomic weight has to be estimated, and the elementary analysis 

 of the acid is to be performed. 



The estimation of the atomic weight is accomplished by heating 

 the fat-acid for some time with half its weight of crystallised 

 carbonate of soda, and with five times its weight of water. 

 Evaporate the saponaceous mass until it be equal to double 

 the weight of the fat-acid employed, treat this with alcohol 

 of 70%, filter, precipitate the filtrate with an aqueous solution 

 of acetate of lead, wash the precipitate, consisting of either 

 oleate or linoleate of lead, by decantation, dry at 110°, and 

 incinerate about 1 gramme carefully in a weighed porcelain 

 crucible. Mix the contents of the crucible, now consisting of 

 oxyd of lead and of metallic lead, after every trace of coal 

 has disappeared, with a few drops of nitric acid of 1 "200, allow to 

 diy carefully at a gentle heat; raise to a red-heat and weigh. 



One hundred parts oleate of lead leave 29-018 oxyd of lead. 



One hundred parts linoleate of lead leave 31472 oxyd of lead. 



Decompose the poi'tion of the lead-soap insoluble in ether with 

 diluted hydrochloric acid warm, fuse the fat-acid obtained repeatedly 

 with warm water until free from lead (tested by sulphuret of 

 hydrogen), dry at 100°, and determine the fusing-point. Now, 

 tUssolve in five times its weight hot alcohol of 90%, keep 

 cold for two days, collect what has crystallised, press, drive ofi" the 

 last traces of alcohol, and determine again the fusing-point. If 

 this coincides with the one obtained before, then the second mass 

 of fat-acid (the lead-compound of which is insoluble in ether) is a 

 single compound; if, contrarily, the second fusing-point is higher, 

 then the crystals have to be recrystallised until a product of a 

 constant fusing-point be obtained. Now, compare this fusing- 

 point with those of the difierent solid fat-acids (lauric, tnyristic, 

 ■palmitic, stearic, and other acids), and see if it agi'ees with any of 

 those (commonly with palmitic acid), when the identity with the 

 latter will be evident. To make sure it is advisable to determine, 

 at least by one experiment, the atomic weight {see above) also, 

 and should this not harmonise, then an elementary analysis has to 

 decide the question. The two latter alterations are indispensable 

 whenever the fusing-point does not coincide with that of any of 

 the fat-acids known as yet. I need scarcely remark that all the 

 other properties of such an acid have also to be investigated. 



If the lead-compound, insoluble in ether and separated from the 

 mixtiu-e of fat-acids, possesses a lower fusing-point than the por- 

 tion crystallised from the alcoholic solution, then at least one 

 other fat-acid is present. To isolate it: mix the alcoholic mother- 

 leys, allow to evaporate slowly, to stand cold during the night, 

 collect eveiy morning what has crystallised and determine the 

 fusing-points. Those crystals formed first are likely to belong to 

 the fat-acid already found before, and must therefore be at once 



