214 



check is necessary, convert this into chloroplatinate of potassium, 

 and estimate the potash from this. 



Suggestions for correcting the Noxious Effects of the Astringent 

 Clay underlying and associated ivith the Greensand, and for 

 using it as a Marl. 



From the descriptions of this stratum already presented, it 

 appears that the action of this astringent mass upon the crop is 

 decidedly pernicious, when the material is employed in any 

 amount beyond the most stinted doses; and the cause of its poi- 

 sonous property would seem, judging from the chemical analyses 

 made, and from other evidence, to be attributable to the acid re- 

 action of the astritigent ingredients which it possesses, namely, 

 the copperas and sulphate of alumina. 



Copperas, though a neutral salt, is well known to chemists to 

 exert an acid reaction, and hence we are not to be amazed that 

 a clay containing it in obvious quantities, should burn, or more 

 strictly poison, the vegetation. Knowing, as we do, the source 

 of the deleterious properties of the clay, a few simple correctives 

 suggest themselves, and such as any one wishing to use this sub- 

 stance as a substitute for marl may adopt. 



My first recommendation to the farmer who is about to make 

 use of this clay upon his soil, is, that he be careful to select, when 

 he has the choice, that variety which contains the green granular 

 material of the true marl, and to avoid altogether the kind which 

 is wholly destitute of this substance. When the green grains are 

 pretty numerous in the mass, as they are near Spotswood, Bur- 

 lington, Camden, and generally upon the northwest side of the 

 marl tract, I would then advise its use, but guarded by the follow- 

 ing precautions. Let the clay be dug several months before it is 

 to be scattered on the land, and let it be spread out in broad, 

 shallow, flat heaps, where the rains may soak through it and carry 

 away the copperas and sulphate of alumina, which, from their 

 well known solubility, will be easily dissolved and washed out. 

 The green mineral does not dissolve in water, and hence, while 

 the rains will purify the mass, no loss of its more active portions 

 can happen. Numerous attempts at using this clay as a marl 

 have shown, that though noxious at first, it is often permanently 



