64 CROP GROWING AND CROP FEEDING 



phoric acid in the form of acid phosphate gave 100 pounds in the crop to 

 every 59 pounds from the Thomas slag, and 8 pounds from the same quantity 

 of bone meal, and in three years the results from the bone meal application 

 were only 17 per cent of those from the acid phosphate. It has been argued 

 by those who favor the use of bone meal that, while not so immediately availa- 

 ble, the after results would more than make up for it. Wagner shows that 

 even after three years it only reached to 17 per cent, of the crop produced at 

 the same time from soluble phosphoric acid. This is an important matter to 

 the fanner, since bone meal is a far more costly article than superphosphate. 

 Aside from the fact of the slow availability of the phosphoric acid in 

 bone meal, there is the further fact that it is very hard to get a perfectly 

 pure bone meal except in States where the inspection is very rigid. The 

 writer once passed an establishment in a large Eastern seaboard city, where 

 the sign announced "pure bone meal." There was a "no admittance" sign 

 at the door, but hearing machinery in operation I ventured to peep in. An 

 Irishman who was tending a machine grinding oyster shells warned me to 

 keep out, but I had seen all that I was after, and noted the place as one to 

 avoid in buying bone. 



THOMAS SLAG, SLAG MEAL, BASIC SLAG AS A SOURCE OF PHOSPHORIC ACID. 



These names, and also the name "odorless phosphate" are applied to the 

 phosphate obtained from the slag made in the process of making steel by 

 what is known as the basic process. There is not enough of it made in this 

 country for it to compete with the rock phosphates. The article is reduced 

 to a fine powder and is not treated with acid. It contains usually about 20 

 per cent, of phosphoric acid in the form of phosphate of lime, or the same 

 form in which it is found in the pulverized phosphate rock. Whether the 

 phosphoric acid in this slag meal is any more readily available than that in 

 the pulverized phosphate rock, or "floats," is a matter not as yet well settled. 

 In most of the country the rock phosphates are cheaper. 



MARLS AS A SOURCE OF PHOSPHORIC ACID. 



The name marl is applied to certain earthy deposits which are found 

 along our Atlantic coast. These vary in composition from those consisting 

 almost entirely of the carbonate of lime from the decomposition of marine 

 shells to those like the green sand of new Jersey and the Virginia marls, some 

 of which contain notable percentages of phosphoric acid and some pot- 

 ash. Phosphatic marls have phosphoric acid in the form of the phos- 



