No. 129.] 331 



is now used extensively by our ocean steamers and others. There 

 is nothing equal to it for painting iron and preserving it from 

 rust J roofs of metal, wire fences, shutters, &c. 



The Secretary read a letter from the Hon. Reverdy Johnson. 

 This letter was in answer to mine, asking if this admirable result 

 of science applied to farming was truly stated in the newspaper, 

 Evening Post of Philadelphia, of July 5th, last. 



The letter of the Secretary to Mr. Johnson, and his reply : 



[From tho Philadelphia Saturday Eyening Post, July 5, 1851.] 



Food for Plants. — A specimen of a soil of good appearance was 

 given to Sir Humphrey Davy, from Lincolnshire, England, as re- 

 markable for sterility. On analyzing it he fuund sulphate of 

 iron. He recommended a top-dressing of lime ; and the sulphate 

 of iron was forthwith converted into the sulphate of lime ; a nox- 

 ious i^ubstance was at once changed into an object of fertility. It 

 was the boast of Franklin that he stripped lightning of its perils 

 and chained the thunderbolt. Chemistry does more. Poisons 

 are changed by its alchemy into the means of subsistence. 



The Hon. Reverdy Jolmson purchased, in 1849, a small farm 

 near Baltimore, in the last stage of impoverishment. Such was 

 its reduced condition that the last crop of corn was not more than 

 one peck to tlie acre. He states that all tlie vegetable matter 

 growing on the two hundred acres of cleared land, including the 

 brier, sassafras and other brushes, if carefully collected, would 

 have been sufficient fur the manufacture of one four-horse wagon 

 load of manure. He applied to Dr. David Stewart, of Ealtimore, 

 an able chemist, who rode out to the farm and procured speci- 

 mens of the soil, which he carefully analyzed. He found that it 

 contained an abundance of lime, potash, magnesia, iron and or- 

 ganic matter, duly mixed with alumina and sand. One element 

 only of a fertile soil was wanting, piiosphoric acid; and of this 

 there was no trace. He recom:nf:'nded an application to ihe soil 

 of the biphosphate of lime, a preparation of bones, as t!ie best 

 mode of supplying the deficient element. The remedy was given 

 at the expense of ten dollars per acre. It was the one thinly 

 needful. Health was restored to the exhausted patient, and the 

 grateful soil yielded laat year twenty-nine bushels wiieat per 



