207 



■solvents, and is put into a glass-flask containing an equal 

 weight of concentrated sulphuric acid, which is diluted with 50 

 times its weight of water; the contents of the flask are then 

 lieated to boil gently. From time to time a drop of the liquid is 

 taken out with a glass-rod and put into a porcelain dish, adding a 

 drop of solution of iodine. When neither a blue nor a violet or 

 reddish colour is produced, the flask is left to cool, the acid 

 liquid (containing the Starch as grape-sugar) is filtered and washed 

 until the acid reaction has disappeared; the liquid is mixed with 

 the water used for washing; saturated (cold) with soda-ley, and 

 its volume ascertained by cubic-centimeters. 



Now, measure from the blue alkaline solution of sulphate of 

 copper, 10 cubic centimeters, pour them into a flask, holding 

 about 100 cubic centimeters, add 40 cubic centimeters water, 

 heat the mixture to a gentle boiling heat, and add of the above 

 neutralised solution of sugar gradually and in intervals, until every 

 trace of blue has disappeared, and in its stead a yellowish tinge 

 is observable. To find out the exact moment of the change of 

 colovir, place the flask on a piece of white pajier. This de- 

 colouration of the cupric solution takes place after 0*05 grammes 

 of grape-siigar, corresponding to 0"045 grammes of starcli, have 

 been added. It is easy herefrom to calculate the concentration of 

 the liquid in question, and its previous amovmt of Starch. The 

 quantity of Starch found in this way has to be added, if necessary, 

 to that obtained before by kneading the substance. 



The sulphuric acid, vised for converting the Starch into grape- 

 sugar, being very diluted, neither vegetable fibrin nor ])ectin 

 which might be present, afiect by changes of theirs the calculation. 



Though, under all cii-cumstances, the Starch is characterised with 

 certainty and precision by its behaviour to iodine; there are dif- 

 ferences of form and size, which to determine demands a micro- 

 scope magnifying at least 400 diameters. Should it not be pos- 

 sible to isolate the Starch, thin slices of the substance, wherein 

 Starch has been indicated by iodine, are submitted to the micro- 

 scopical examination. 



Stearic Acid = Cse H35 3 + HO. Contained as tristearin 

 in fats, especially solid ones. Saponify with soda-ley, decompose 

 the soap with hydrochloric acid, dissolve the fixt-acids in hot 

 alcohol, allow to crystallise, press and recrystallise repeatedly, 

 until the product fuses at 69-1° to 69-2°. Shea-butter is of all 

 vegetable and animal fats the best adapted for preparing pure 

 steai'ic acid, as it contains only the one solid fat-acid. — Forms 

 pearly needles and leaflets, inodorous and tasteless, of perceptibly 

 acid reaction, fuses at 69-1° to 69-2°, has at 9° to 11° a density 

 of 1-000, boils and distils in a vacuum unaltered, is not soluble in 

 w^atei', dissolves in 40 paits cold absolute and in every proportion 



