36 Journal of the Department of Agriculture. 



Limits. 



In Reg-ulation No. 24 a table of limits is given, and it is provided 

 that " fertilizers and farm foods shall be deemed to be sufficiently in 

 accord with the guaranteed or reg'istered composition if upon analysis 

 the actual percentages be found not to fall below those stated in the 

 invoice or in the certificate of registration by more than the limits set 

 forth in this regulation." 



This regulation requires some little explanation. At first sight 

 it would appear that a vendor is permitted to register and invoice a 

 certain quantity of any constituent over and above the quantity 

 actually contained in the fertilizer. The "limit" fixed for total 

 phosphoric oxide in bone meal, for example, is 1 per cent. ; if a sample 

 of bone meal, registered and invoiced as containing 24 per cent, of 

 phosphoric oxide, were found upon analysis to contain 23 per cent, it 

 would be " deemed to be sufficiently in accord with the guaranteed or 

 registered composition." This does not mean, however, that the 

 buyer, in assessing the value of a fertilizer, must take the limits into 

 consideration ; he must not argue that if 18 per cent, of phosphoric 

 oxide in superphosphate is guaranteed he can only count on getting 

 an article containing 17.5 per cent, (the limit in this case is 0.5 per 

 cent.). It is true that a vendor might increase the guaranteed 

 amount by the limit with intent to defraud, but this is unlikely, as a 

 study of the reasons for fixing the limits will show. It must be 

 remembered in the first place that fertilizers and farm foods are, as a 

 rule, sold in comparatively large quantities, that a sample taken for 

 analysis is small (it is fixed by regulation as of about 6 lb. weight), 

 and that the actual portion analysed by fhe analyst is much smaller 

 still. It is obvious that if two different samples are analysed exactly 

 the same analytical results will only be obtained if the material is 

 perfectly uniform. Uniformity of two or more samples is aimed at 

 by the method of sampling prescribed by Regulation No. 22, but 

 absolute uniformity is difficult of attainment. The vendor, if he 

 employs a mixing process, tries to make tlie article as uniform as 

 possible. He must do this because for application to the soil a 

 fertilizer must be uniform, since the farmer would be very dissatisfied 

 if he found after the fertilizer had been distributed that all the active 

 ingredients were concentrated on one portion of the land while the 

 other portion had received little or none. The crop would probably 

 suffer on both portions. 



The person taking the sample also tries to secure uniformity by 

 taking portions from several packages, mixing these well, and then 

 taking a portion of this mixture. This process is repeated by the 

 analyst in "sampling down," as it is called. Certain articles are 

 manufactured in a very uniform condition, others can easily be mixed 

 to a high degree of uniformity, others again are extremely difficult to 

 mix so as to secure reasonable homogeneity. This is taken into 

 account in fixing the limits, which are not the same for all classes of 

 fertilizers and farm foods. Another source of any difference there 

 may be in the analyses of two samples is the analytical error. There 

 is always a certain amount of experimental error in analytical pro- 

 cesses. These are not performed with the absolute mathematical 

 precision of a machine. Part of the error is due to the method 

 employed in the analysis. Few. if any, analytical processes are 



