A known quantity of the solution to be tested, containing acetone to the extent of 0.1 to 0.2 grm., is pipetted into a 500 c.c. round-bottom flask, diluted with a little water, and mixed with 20 to 30 c.c. of a 10 per cent. solution of caustic potash.  The flask is connected with a long reflex condenser, and is also fitted with a dropping funnel containing a solution of bromine in potassium bromide (200 grms. of Br and 250 grms. of KBr to 1 litre of water).  The bromine solution is allowed to flow into the mixture until it has acquired a faint yellow tinge, the flask and its contents being then heated on the water bath at about 70 deg.  C. for half-an-hour.  Bromine solution is added drop by drop until the slight coloration is permanent, excess of bromine being got rid of by boiling for a minute or two with a little more caustic potash.  The mixture is then distilled until the distillate is free from bromoform, halogen being tested for in the usual manner.  Water is added to the contents of the flask if necessary.  It may be here observed that no acetone can be detected in the distillate by means of the mercuric oxide test, and free bromine is also absent.  The condenser having been washed out with a little alcohol, in order to remove any traces of bromoform which may have collected, the distillate and washings are mixed with 50 c.c. of alcohol and sufficient solid caustic potash to make an approximately 10 per cent. solution.  The mixture is then heated on the water bath under a reflux condenser until the bromoform is completely decomposed.  This generally occupies about three-quarters of an hour.  The liquid is allowed to cool, evaporated to smaller bulk if necessary, and exactly neutralised with dilute nitric acid.  It is then diluted with water to 500 c.c., and an aliquot part titrated with N/10 silver nitrate solution, using potassium chromate as indicator; 240 parts of bromine correspond to 58 parts of acetone.  The complete analysis can be performed in one and a half to two hours.  It is imperative that the bromine used should be pure, as crude bromine frequently contains bromoform.  The method is suitable for the estimation of acetone in wood-spirit, the spirit being diluted to 10 times its volume, and 5 c.c. of this solution employed for the determination.  For example—­

(1.) Three c.c. of a solution containing 9.61 per cent. acetone gave 1.7850 grm.  KBr.  Acetone found = 9.66 per cent.

(2.) Ten c.c. of a solution containing 0.96 per cent. acetone gave 0.5847 grm.  KBr.  Acetone found = 0.95 per cent.

Nitro-Cotton.—­The first thing upon opening a case of wet cotton, or in receiving a sample from the “poacher,” that requires to be determined is the percentage of water that it contains.  It is best done by weighing out about 1,000 grms. upon a paper tray, which has been previously dried in the oven at 100 deg.  C. for some time, and become constant in weight.  The trayful of cotton is then placed in a water oven, kept at 100 deg.  C., and dried as long as it loses water.  The loss gives the percentage of water.  It varies from 20 to 30 per cent. as a rule in “wet” cotton.