318 Scientific Intelligence. [ApRIL, 
manganese has the same property of absorbing various doses of 
oxygen; but have not yet heard whether it be capable of furnishing 
it to the roots of plants. Sir H. Davy, I think, says that oxide of 
iron is very useful in vegetation ; but of oxide of manganese he has 
not said a word. Should you think it worth your while, you will 
much oblige a constant reader, and numerous others who are en- 
gaged in clay-burning, by explaining what you conceive to be the 
benefit derived from this process. J have seen some fields having 
had the whole surface ploughed up, being a clay soil, and a good 
deal of vegetable remains mixed with manure, subjected to this 
wasteful torrefaction. Manure in Scotland is difficult to be had, 
and the management of it not at all understood. Surely this 
method of destroying it in the soil is most wasteful, and will finally 
prove highly injurious to the interests of agriculture. if not soon 
checked. If at any time you should find leisure, some papers on the 
management and preparation of manure on sound chemical prin- 
ciples, introduced into your publication, would be well received by 
your northern friends. With hopes of soon seeing your attention 
given to the explanation, and what you conceive may be the advan- 
tages of clay-burning, 
I remain, dear Sir, 
A Constant READER. 
I am sorry that I am quite unable to give a satisfactory explanation 
of the practice alluded to in the preceding letter. On reading 
Mr. Craig’s letter on the subject, when in Edinburgh last year, I 
made some inquiry about it, and was informed (I think) by Pro- 
fessor Jameson that he had seen some specimens of the clay thus 
burnt, and that in reality it was a marl. ‘This explanation satisfied 
me at the time; but it is quite obvious, if the sub-soil from Port 
Patrick to Berwick be treated in this manner, that its nature must 
vary greatly in different places. 
The burning of clay as a manure is not a new discovery, as it is 
supposed to be, in the Farmer’s Magazine. Dr. Reid, in a Jetter to 
Lord Kames, written in 1775, says, “ If wet clay is put into the 
fire uncompressed, 1 am informed that it burns to ashes, which 
make no bad manure.” (Life of Lord Kames, vol. iii. p, 224.) 
We can assign some conjectural advantages that may result from 
burning clay, and laying it as a manure on clay land. From the 
curious table by Dr. Schibler, inserted in the last number of the 
Annals (p. 208), we see how very adhesive (or heavy, as agricul- 
turists term it) clay soil is, and how strongly it retains moisture. 
Now when clay is burnt it loses these qualities. Such a mixture, 
therefore, may tend to render a clay soil less adhesive, and less re- 
tentive of moisture; but if this be its only use, fine sand or calca- 
reous sand would probably answer better. 
From Mr. Craig’s description of the burning, we may infer that 
the heat applied is very smzll; for he says that the combustion is 
not apparent, unless you open up the heap; and that in such a case 
