70 METHODS OF ANALYSIS. 



filter and precipitate the tin from this solution with hydrogen sulphid ; wash 

 the precipitate on a filter and dissolve it in an excess of ammonium sulphid. 

 Filter this solution into a tared platinum dish and deposit the tin directly in 

 the dish by electrolysis, using a current of 0.05 ampere. This current may be 

 readily reduced from an ordinary 110-volt street circuit by means of a series 

 of lamps, or a rheostat may be improvised for this purpose, consisting of a long, 

 vertical glass tube, sealed at the bottom, containing a column of dilute acid 

 through which the current passes, the resistance being changed by varying 

 the length of the acid column contained between two electrodes immersed 

 therein, one of which is movables 



4. Nitrogen. Provisional. 



Determine in 5 grams of the sample by the Kjeldahl or Gunning methods, 

 page 5, under " I. Fertilizers." 



5. Sucrose. Provisional. 



Calculate sucrose from the polarization & before and after inversion, as 

 directed under " VI. General Methods," page 41. In case of confectionery con- 

 taining insoluble matter employ the double-dilution method^ thus making due 

 allowance for the volume of the precipitate, as follows : Use half the normal 

 weight of the sample and make up the solution to 100 cc, employing the appro- 

 priate clarifier (subacetate of lead for dark-colored confectionery or molasses 

 and alumina cream for light-colored confectionery and honey). Use the normal 

 weight of the sample and make up a second solution with the clarifier to 100 cc. 

 Filter and obtain direct polariscopic readings of both solutions. Invert each 

 in the usual manner and obtain the invert readings of the two. 



The true direct polarization of the sample is the product of the two direct 

 readings divided by their difference. 



The true invert polarization is the product of the two invert readings divided 

 by their difference. 



C. Commercial Glucose in Molasses, Sirups, and Honey. <* (Approximate 



Method). Provisional. 



It is manifestly impossible to determine with absolute accuracy the amount 

 of commercial glucose present by reason of the varying amounts of dextrin, 

 maltose, and dextrose present in the adulterant. It is possible, however, in 

 sirups, in which the amount of invert sugar is so small as not to appreciably 

 nffect the result, to estimate approximately the amount of commercial glucose by 

 the following formula : 



r-fa-S) 100 

 -175 



Wiley, Principles and Practice of Agricultural Analysis, 8: 152. 



&A11 products, such as honeys, sirups, etc., which contain dextrose or other reducing 

 sugars In the crystalline form or in supersaturated solution, exhibit the phenomenon of 

 birotation. The constant rotation only should be employed in the Clerget formula, and to 

 obtain this the solutions prepared for direct polarization should be allowed to stand over 

 night before making the reading. In case it is desired to make the direct reading imme- 

 diately the birotation may be destroyed by heating the neutral solution to boiling for a 

 few minutes or by adding a few drops of strong ammonium hydroxid before completing 

 the volume. 



Wiley and Ewell, Analyst, 1896, 21: 182. 



* Leach, Thirty-second Ann. Kept. Mass. State Board of Health, 1900, p. 658 ; reprint, 

 p. 42. 



