fURITY 619 



mean the difference between a paying crop and one which is 

 grown at a loss. Even when the seed supplied is guaranteed to 

 be that of a particular strain, say ' Nonsuch,' it is to be noted that 

 it may have degenerated or altered considerably since its first 

 issue by the raiser (see p. 317). 



Nothing short of actual trial of the seed on the land will 

 determine differences of this character, and it is therefore 

 necessary to trust to the reputation of the vendor. 



The apparatus needed to determine the purity of samples 

 are : (i) a good chemical balance ; (2) a small spoon or spatula; 

 (3) a series of sieves of different-sized meshes ; (4) three or 

 four porcelain dishes and a dozen watch glasses of different 

 sizes ; (5) two or three sheets of black and white cardboard or 

 stiff paper ; and (6) a good pocket lens or microscope with low 

 powers. 



Ex. 275. — Determine the purity of the sample of red clover seed. Weigh 

 out about 20 grams of the seed and carefully sift it through the sieves 

 to separate any impurities present which differ in size from the clover 

 seeds. Place these on one side in a porcelain dish. Spread the rest of the 

 sample on a sheet of cardboard and examine it with the naked eye and the 

 lens for impurities which escape the screens. Any which are obtained must 

 be added to the impurities in the porcelain dish and then carefully weighed 

 on a watch glass. From the weight of the sample taken, and the weight 

 of the impurities in it, the percentage purity can be calculated thus : — 



Grams. 

 Weight of seed taken = ...... 1672 



Weight of impurity obtained = 0"54 



Pure seed = i6'i8 

 The percentage of pure seed, or the amount by weight in 100 lbs. of the 

 sample is 



i6'i8x 100 , „o/ 

 1672 =^^^^° 

 that is to say in 100 lbs weight of seed purchased there is over three lbs of 

 useless material. 



Examine the nature of the impurity obtained, and determine whether it is 

 inert material such as dead husks, chaff, and dirt, or seeds of weeds. A 

 record should be made of the number of weed seeds present. 



