THE DETERMINATION OF CANE SUGAR 521 



the lead followed by calcium carbonate to neutrality and made up to 200 c.c. 

 After filtering, aided if necessary by alumina cream or kieselguhr, the direct 

 reading is observed; 50 c.c. of this filtrate is heated with 0-5 gram pressed 

 yeast at 55° C. for 4^ hours, made up to 55 c.c. and filtered. This material 

 serves to give the inverted reading. 



Hudson^* has worked out the following routine for preparing an invertase 

 of great activity : — 



" To prepare a stock solution of invertase, break up 5 lbs. of pressed 

 yeast, which may be either bakers' or brewers' yeast, add 30 c.c. of chloroform 

 to it in a closed flask, and allow it to stand at room temperature over night. 

 By morning the solid mass will have become fluid and it should then be filtered 

 through filter paper, allowing several hours for draining. To the filtrate add 

 neutral lead acetate until no further precipitate forms, and again filter. 

 Precipitate the excess of lead from the filtrate with potassium oxalate and 

 filter. To this filtrate add 25 c.c. of toluene and dialyse the mixture in a 

 pig's bladder or collodion membrane for two or three days against running 

 tap water. The dialysed solution is colourless, perfectly clear after filtra- 

 tion, neutral to litmus, has a solid content of about half of i per cent., an 

 ash content of a few hundredths of i per cent., will keep indefinitely in an ice 

 box, if a little toluene is kept on its surface to prevent the growth of micro- 

 organisms, and is exceedingly active in inverting cane sugar. This invertase 

 solution does not reduce Fehling's solution." 



Of this preparation 5 c.c. is used. Hudson performs the inversion at 

 room temperature and effects the de-leading with potassium carbonate or 

 oxalate. 



In both these schemes, the rate of inversion is very much increased, as was 

 shown by O'Sullivan, by the simultaneous presence of very small quantities 

 of free acid. Hudson states that the maximum activity with hydrochloric 

 acid occurs at a concentration of one-thousandth normal. 



In the method proposed by the writer^® the solutions required are those 

 of the alumina-baryta method of defecation given earlier in this chapter. 

 To 50 c.c. of material the stated quantity of aluminium sulphate and sul- 

 phuric acid is added, after which the flask and its contents are immersed in a 

 bath of boiling water for 30 minutes to obtain inversion. After cooling, the 

 defecation is then made by the addition of the exact equivalent of baryta, 

 and then, after completing to volume and filtering, the reading in the polari- 

 meter is made. This method has not yet been subjected to independent 

 critical examination. 



Both of these methods require the determination of the Clerget divisor. 

 Ogilvie found 1-416 as the value for 13 grams in 100 c.c. Both Browne and 

 Jackson and Gillis incline to i • 420 as the value, and introducing the factor 



t 

 for concentration the probable value should be 142 • o -f-o • 0676 (w— 13) 



where m is the number of grams sucrose per 100 c.c. and t is the temperature. 



Methods depending on the Destruction of Reducing Sugars. — Dubrunfaut^^ 

 first observed that reducing sugars heated with alkalies tended to give a 

 product almost inactive optically, and proposed the application of this ob- 

 servation to analyses. Two later applications are described below. 



Pellet and Lemeland's Method.^'' — Fifty c.c. of a solution of molasses, 

 containing not more than 5 per cent, of reducing sugars, are transferred 

 to a 300 c.c. flask. To this is added 7-5 c.c. of caustic soda of 36° Baume 



