AGRICULTURAL CHEMISTRY — AGROTECHNY. Ill 



iilroiuly been mentioned (E. S. E., 10, p. 840) and used in work in-eviously de- 

 scribed (E. S. R., 22, p. 238). 



In detail it is as follows: "Place 12 gni. of material in a 300 cc. graduated 

 fiask," add 150 cc. of 50 per cent alcohol by volume (carefully neutralized), 

 mix thorougbly, and boil on a steam bath for 1 hour, using a small funnel in 

 the neck of the flask to condense the vapor. Then cool. If desired, allow it to 

 stand overnight. Make up to volume with 95 per cent alcohol (neutral in reac- 

 tion), mix thoroughly, allow to settle, transfer 200 cc. to a beaker with a 

 pipette, and evaporate on steam bath to a volume of from 20 to 30 cc. The 

 presence of a trace of alcohol is not harmful. Do not evaporate the solution to 

 dryness. (By evaporating the 200 cc. portion in a short-necked, ballon-shapeil 

 distilling flask, connected with a condenser. 75 to SO per cent of alcohol can be 

 recovered before the material in the flask foams violently. The short neck — 

 1 in. — of these flasks makes it possible to remove the residue easily. The 100 

 cc. remaining in the digestion flask may be strained through a cotton bag 

 and the alcohol recovered from the liquid as just described. This is easily 

 accomplished and results in a marked saving when a large number of samples 

 are run.) Transfer the contents of the beaker or flask, as the case may be, to 

 a 100 cc. graduated flask, washing thoroughly with water. Add enough of a 

 saturated solution of neutral load acetate to produce a flocculent precipitate 

 and allow to stand 15 minutes. 



"At this point the solution may safely stand overnight if desired. Make up 

 to the mark with distilled water and pass through a folded filter, carefully 

 saving all of the filtrate, to which add enough anhydi'ous sodium carbonate to 

 I)recipitate all the lead, allow to stand 15 minutes, and pour onto an ashless 

 filter. Over 75 cc. of filtrate should be obtained. Test the filtrate for lead with 

 a small quantity of dry sodium carbonate, and if any precipitation occurs add 

 more anhydrous sodium carbonate and refilter. Use 25 cc. of this clear filtrate 

 together with 25 cc. of water for the determination of reducing sugars by the 

 method of Munson and Walker. In a 100 cc. graduated flask, place 50 cc. of 

 the same filtrare, add a small piece of litmus paper, and neutralize with acetic 

 acid ; then add 5 cc. of concentrated hydrochloric acid and let stand overnight 

 for inversion. (Standing 48 hours does not apparently affect the results.) 

 Then pour the inverted solution into a 400 cc. beaker and neutralize with 

 anhydrous sodium carbonate; return it to the 100 cc. flask and make up to the 

 mark. Filter, if necessary, and use 50 cc. for the determination of total sugars 

 as invert by the method of Munson and Walker. 



"The amount of cuprous oxid or copper obtained in either the reducing or 

 the total sugar determination represents the sugar contained in 2 gm. of the ma- 

 terial. Therefore the weights of the invert sugar when divided by 2 and multi- 

 plied by 100 give the respective percentages of sugar as invert. Subtract the 

 l)ercentage of reducing sugars before inversion from the percentage of total 

 sugar after inversion, both calculated as invert, and the difference multiplied by 

 0.95 gives the percentage of sucrose. Since the insoluble material of the grain 

 or cattle feed occupies some space in the flask as originally made up, it is neces- 

 sary to correct for this volume. Results of a large number of determinations on 

 various materials have shown the average volume of 12 gm. of material to be 

 9 cc. ; therefore the correction factor for 12 gm. in 300 cc. is 0.97, and the per- 

 centage figures for reducing sugar and sucrose are to be multiplied by this factor 

 to obtain the true amounts." 



« If the material is acid in reaction, it would be well to add from 1 to 3 gm. 

 of precipitated calcium carbonate to neutralize the acidity. 



