8 



at least 150 per cent excess of lead is required to obtain the maximum 

 precipitation and, further, that 250 per cent excess of lead has prac- 

 tically a negligible effect in preventing the maximum precipitation. 



In analyzing a series of unknown sirups it would be impracticable 

 to ascertain by preliminary trial the desirable amount of lead to be 

 added and then to introduce these varying amounts into each test; 

 furthermore, proportional values are not obtained even by varying 

 the amounts of lead. The modified method, however, as given in 

 the following section appears to give satisfactory proportional results 

 on sirups of varying composition. 



PROPOSED MODIFICATION. 



To overcome the solvent or disturbing action of the sugar, it 

 occurred to the writer that the addition of a precipitant, such as 

 potassium sulphate solution, would allow a more complete formation 

 of the maple lead precipitate and give proportionate results. Sev- 

 eral series of experiments were made to ascertain the amount of 

 potassium sulphate which should be added to correct the solvent 

 action of the sugar, and the following method was adopted: 



Transfer 25 grams of the sirup to a 100 cc flask, using about 25 cc of distilled water, 

 add 10 cc of potassium sulphate solution (7 grams per liter); then 25 cc of lead sub- 

 acetate solution of the strength specified by Winton. Make up to the mark, shake 

 thoroughly and allow to stand three hours. Filter, rejecting the first portion of the 

 filtrate. Pipette off 10 cc of the clear filtrate into a 250 cc beaker, dilute to 50 cc, add 

 2 cc of 20 per cent sulphuric acid and 100 cc of 95 per cent alcohol. Let stand over 

 night; filter off the lead sulphate on an ignited, weighed Gooch crucible, wash with 

 95 per cent alcohol, dry, ignite at low redness for three minutes in a muffle or over a 

 burner, taking care to avoid reducing cone of the flame, and weigh. Run a blank in 

 exactly the same way substituting 25 grams of a pure cane sugar sirup (66 per cent 

 sucrose content) in place of the sirup to be tested, b Subtract the weight of the lead 

 sulphate, obtained from 10 cc of the sirup test filtrate, from that obtained from 10 cc 

 of the cane sugar sirup blank filtrate. The remainder, expressed in grams and 

 multiplied by 27.325 gives the modified Winton lead number. 



The precipitate formed in the blank was very slight, little more 

 than an opalescence, while in the mixed sirups the volume of pre- 

 cipitate was proportional and a marked flocculent precipitate was 

 observed in the 10 per cent maple content sirup. The flasks should 

 be rotated gently when water is added to make up to mark, otherwise 

 the sugar solution becomes too weak. When water is floated on the 

 contents of the flask a slightly increased precipitation of lead sulphate 

 is produced, which is not redissolved on subsequent agitation. 



The lead number's obtained in this way on straight maple sirups are 

 somewhat higher than by the original method, 1.8 to 3 instead of 1.2 



Freshly boiled distilled water should be used throughout. 



& Do not use acetic acid in this blank; acidified blank is suggested for use only with 

 original Winton method. 

 [Cir. 53] 



