12 PROCEEDINGS OF THE ASSOCIATION OF 



were offered, and facts stated by Mr. Martin H. Bo ye, Drs. 

 Charles T. Jackson, James B. Rogers, J. Locke, and Mr. B. 



SiLLIMAN, Jr. 



Ml*. BoYE inquired whether the antacid powers of magnesia, 

 and its effects on vegetation, had been noticed, as it exists in the 

 dolomitic limestone. 



Dr. Jackson infen-ed from his observations, that magnesia is 

 injurious only when used in a caustic slate, in the same manner 

 as caustic lime is known to be injurious to vegetation by ab- 

 stracting carbonic acid from the atmosphere, and from decompos- 

 ing vegetable and animal matters. It also acts unfavorably in 

 virtue of its hydraulic power; rendering, in some cases, the soil 

 very hard. He further stated, that when composted with peat and 

 swamp muck it gained from these substances phosphoric acid, and 

 thus became the means of conveying to wheat and other cereal 

 grains the phosphate of magnesia, known to be always found in 

 their ashes. Dr. Jackson further considered the combinations of 

 lime with the organic acids of soils as deserving much attention. 

 He had found sub-soils to contain a larger quantity of crenates of 

 lime than the soil, and that some streams in like manner con- 

 tained a larger proportion of soluble crenates than others ; and 

 these former are most valuable for the purposes of irrigation. Dr. 

 J. recommends the employment of a compost of lime, swamp 

 muck or peat, and animal manure ; and he attributes the benefi- 

 cial effect of this in part to tlie evolution of ammonia consequent 

 upon the decomposition of the organic matters. 



The discussion then turned on the character of hydrated perox- 

 ide of iron on vegetation. It was thought by Dr. Jackson, that 

 the injurious effects sometimes known to arise from it were to be 

 attributed to free sulphuric acid contained in it from the decom- 

 position of suli)huret of iron. A marl was cited which at first 

 produced very luxuriant vegetation, but at a subsequent period 

 was found to destroy the plants growing where it had been used, 

 owing to the decomposition of sulphuret of iron contained in it, 

 producing free sulphuric acid, which coiToded the plants. Prof. 

 H. D. Rogers, thought that some of the marls of New Jersey, 

 contained so much sulj^huret of iron as to require more alkaline 

 matter than was to* be found in them to neutrahze the acid result- 

 ing from their decomposition. Still it was thought that small 

 quantities of sul)>huret of iron, in a marl, would by its decompo- 

 sition be useful in agriculture. 



The subject of potash in soils was next brought before the 

 meeting. Dr. Jackson inquired if any experiments had been 



