INSPECTION OF COMMERCIAL FERTILIZERS 51 



the first year, a plant food valuation of only 69 cents could be given on a ton of the 

 product. The ton cost varied from $35 to $45. 



Colloidal Phosphate. 



This product was temporarily registered in Massachusetts as Florida Phosi)liate 

 with Colloidal Clay. Later, through mechanical separation of the product supple- 

 mented by a chemical analysis of the varioiis separated portions, both made at this 

 institution, it was determined that the material was largely of a colloidal nature 

 (having diameter of particles from .005 to .0001 mm.). Registration has since 

 been completed under the name Colloidal Phosphate. 



This product is a low-analysis natural Florida phosphate known to the industry 

 as "pond phosphate," a by-product in mining Florida rock phosphate. In the 

 recovery of this Florida rock phosphate, water is used. The soft, finely divided phos- 

 phate, with more or less clay and silt, is washed into ponds or basins, the finer 

 material separating more abundantly at points farthest from the washer. When 

 the water evaporates, the very finely divided deposit reinains, and this is the source 

 of the product under discussion. 



The material is not sufficiently rich in phosphoric acid and, moreover, contains 

 too much iron and alurnina to warrant its use in the manufacture of superphos- 

 phate. Its use as a fertihzer is therefore restricted at present to direct application 

 to the soil. The product is in no sense a complete fertilizer as it contains no 

 nitrogen or soluble potash, but furnishes phosphoric acid in the form of tri- 

 calcium, iron and alumina phosphate, forms considered unavailable according to 

 official methods of analysis. 



With reference to its purchase as a source of phosphoric acid, without considera- 

 tion of the claims of the producers as to merits based on its colloidal nature or any 

 unique feature of its chemical composition, it might be compared to superphos- 

 phate. The more common grade of superphosphate sold in Massachusetts 

 contains 16 per cent available phosphoric acid of which from 9 to 11 per cent is 

 in water soluble form. This product cost on the average during 1929, $20 per ton, 

 deUvered, thus making the unit cost of available phosphoric acid from this source 

 $1.25, which is at the rate of 6)^ cents per pound. The colloidal phosphate 

 is guaranteed 22 per cent total phosphoric acid, no claim being made for either 

 water soluble or available phosphoric acid. The ton price quoted for the product 

 is $55, f.o.b. Boston, thus making the unit cost for (otai phosphoric acid $2.50, 

 which is at the rate of 12^/2 cents per pound, or more than double the cost from 

 superphosphate. 



This Station has made two analysis of the colloidal phosphate, with results as 



follows: • • , 



Total phosphoric acul. 



Sample received from Natural Products Corp. 20.40 



Sample received from Market Garden Field Station 21.18 



The product was registered under a guarantee of 22 per cent total phosphoric 

 acid, no claim being made for water soluble or available phosphoric acid, nitrogen 

 or potash. Our analyses, therefore, did not include these determinations. The 

 variations noted in the composition of the two samples as compared with the 

 guarantee are not surprising, as such a product is hkely to vary in composition, and 

 it would hardly be an economical proposition to attempt its standardization. 



DEFINITIONS AND INTERPRETATIONS REGARDING 

 FERTILIZERS. 



The following definitions and interpretations were adopted as official by vote of 

 the Association of Official Agricultural Chemists at a recent meeting held in 

 Washington. 



