297 



Tlie fat, freed from all resin, lias now to be weighed, and to be 

 studied in respect to its external characteristics, colour, smell, and 

 taste; of fats solid at ordinary temperature the fusing- jwint is to 

 determined (see Div. II., C, «), of fats liquid at ordinary tempera- 

 ture the freezing-point, and of both the specific gravities in the 

 liquid state, and the temperature when thus examined ; try also 

 the solubility in ether, alcohol of 100 and of 90 %, benzol, chloro- 

 form, wood-spirit, sulphide of carbon, petroleum, and in oil of 

 turpentine at ordinary temperature and when heated ; spread also 

 thin layers of the fat on a glass-plate, and see whether it will dry 

 or not after being left for not less than a fortnight at a mean tem- 

 perature ; and lastly, try its behaviour towards concentrated 

 mineral acids and caustic alkalies. 



Should a saponification have been effected by means of any 

 fixed alkali, then from a weighed quantity of the fat a soap is to 

 be formed (with an alkali free from chlorides and nitrates), and to 

 be decomposed by adding an excess of dilute sulphuric acid and 

 digesting at a gentle heat (below the boiling-point of water), then 

 allow the mass to stand cold, perforate the hard layer of fat-acids («), 

 pour ofi" the acid aqueous liquid (6), wash repeatedly by adding 

 fi'esh water, digest, set aside into the cold, perforate, and pour off' 

 the water, and examine the fat-acids according to a, and the 

 united acid liquids according to h. 



(a) The mass of fat-acids obtained, is always a mixture of one 

 liquid and of one or seveiul solid fat-acids. After determining the 

 fusing point of this mass, add one and a-half times its weight 

 pure white of lead, triturated with water to a fine pulp, digest 

 for a few hours under frequent stirring and at about 100°, transfer 

 the lead-soap to a wide-mouthed bottle, add about five times its 

 weight ether, secure the bottle with a coi"k stopper, shake with 

 care lest any of the contents should get into the neck, filter after 

 24 hours into a larger bottle, wash the remaining portion of solid 

 fat-acids combined with lead with ether as long as it dissolves 

 anything, mix the united ethereous filtrates Avith hydrochloric acid 

 and shake for a few minutes. After the chloride of lead has sub- 

 sided, try if a sample of the ethei-eous liquid, mixed in a test-tube 

 with sulphuret of hydrogen, and well shaken, will assume a brown 

 or a black colour ; if so, add again hydrochloric acid, shake, let 

 subside, and test again with sulphiiret of hydrogen. Filter the 

 •ethereous liquid, after the wliole of the lead has been precipitated, 

 into a glass beaker, and drive off" the ether by exjjosure to the open 

 air and the rest by means of the air-pump. 



The fat-acid remaining in the glass beaker is now probably 

 either oleic acid, obtained from non-drying oils, or linoleic acid, 

 which is the liquid constituent of most drying oils. Should the 

 fat-acid diff'er from either oleic or linoleic acid, its peculiar 

 properties have to be further investigated; besides, now the 



