338 Chemical Changes in the Fermentation of Dung. 
substance can putrefy without evolving it. The only question 
•which it appears possible to raise is Jlow much is thus dissipated, 
and whether it be of sufficient practical importance to need a 
remedy. 
That it may be much will I think be admitted by all who 
weigh the following consideraticms. First : tiiat phosphorus does 
not exist in plants merely as the fixed substance phosphoric acid 
may be shown from the case of coal. I never remember seeing 
an analysis of coal which included phosphoric acid among its 
constituents. Professor Johnston indeed in his ' Elements of 
Agricultural Chemistry,' p. 224, ed. 5, does include phosphate of 
lime among the substances found in coal ashes, but it seems to 
be mentioned rather as what must or ought to he than as ^chat is. 
In a book published recently by a well-known chemist. Dr. R. D. 
Thompson, under the head of Coal we find these words ; " Coal 
appears to contain a small quantity of phosphoric acid although 
we might expect it to contain it in greater quantity, if coal is a 
substance of vegetable origin as is the opinion universally enter- 
tained." This may fairly be taken to represent what is known 
upon the subject. But I have got both phosphuretted hydrogen 
and phosphoric acid in considerable quantity by the distillation 
of coal. 
Now this portion of phosphorus can hardly exist in coal as 
pliosphoric acid, for if it did some of the many able analysts who 
have sought to ascertain the inor<ranic substances in coal would 
have discovered it. But if it do not exist thus in coal neither it 
would appear did it in the plants from ichich coal is formed, for it 
is difficult to conceive that the deoxidizing process can have been 
carried far enough in ordinary bituminous coal (which contains 
about 10 per cent, of oxygen) for phosphoric acid to have been 
robbed -of its oxygen. The only conclusion therefore to which 
we can come is that phosphorus existed in the coal plants in a 
form capable of volatilization, and therefore diffijrent from that of 
its ordinary combination with oxygen as phosphoric acid. 
The laws of nature are too fixed to allow us to suspect differ- 
ences in her processes thougli thousands of years may intervene 
between the periods at which we study them, so that we have 
strong apriori ground for thinking that what existed of old exists 
now. The argument would be incomplete unless the reader 
were reminded that nascent hydrogen has the power of deoxidizing 
phosphoric acid, the most stable of the compounds of phos- 
phorus, and of uniting itself witli the liberated phosphorus to 
form the volatile compound phosphuretted hydrogen. If phos- 
phoric acid be placed in a flask with zinc and dilute sulphuric 
acid the stable compound will be broken up and the volatile 
phosphuretted hydrogen formed instead. The reader will also 
