VoL. III. 
AUGUSTA, GA., OCTOBER, 1845. 
No. 10. 
AGRICSJIiTrrRAI. IIVSTRTJCTSOIV IIV 
COMMO-'V SCHOOLS. 
PROF. Johnson’s second lecture. 
On Saturday, according to promise, Mr, 
Johnston delivered a second lecture in the same 
place, Mr. Taylor, ol Duddingston School, oc- 
cupying the Chair. 
Mr. Johnston said — Gentlemen, at the close 
of my address to you yesterday, I told you that 
I thought that \,vhat I said would not possess 
the same weight, or appear to have the same 
importance to you as to the practical agricultur- 
ist, and that you could not by any means feel 
the like interest that I feel, because in all proba- 
bility most of )’ou are unacquainted with the 
way in which agricultural chemistry bears up- 
on, and IS advantageous to, the practical agri- 
culturist of the country. It was for that reason 
that I offered to give you an exposition of most 
of the important points in the science — to give 
you a short sketch, a sort of bird’s-eye view, of 
that interesting branch of knowledge, to induce 
you to te.ach which, I presented to you so many 
considerations yesterday; and lam confident 
that when you have formed an idea of the sub- 
ject, you will find it most interesting, and one 
which will yield you great satisfaction and 
pleasure to become acquainted with. Gentle- 
men, there was a time when this hill upon 
which we now stand was nothing but a naked 
rock of lava. That old lava gradually decayed 
as modern lavas do, and crumbled down and 
formed loose matter on the surface, in which 
seeds of plants grew, died, andlefttheir remains. 
Thus by degrees the soil accumulated to such 
as you now see on the surface of this rock, on 
which plants nowgrow. Such is the history of 
nearly all the soils on the surface of the globe. 
Suppose you take a portion ol any one soil j 
and put it upon the end of a piece of metal, such j 
as ] am doingjust now, and in any way expose i 
it to the action of the fire, you will see that part | 
of the sol! will grow blacker at the edges; bye j 
and bye that blackness will disappear, and the | 
soil will assume a color more or less dark, ac- j 
cording t© the nature of the substancesof which 
that which remains consists. If you take this 
portion of the soil before it is heated and weigh 
it, you will find that after it is exposed to the 
fire it is not so heavy as before. That portion | 
of the soil which has burned away consists of 1 
the remains of those vegetablesof which I have j 
spoken; of those animals who have died and ; 
been deposited in the soil ; and of the manures | 
which have been applied by the farmer. Thus ! 
vegetable matter forms what is called the organ- j 
ic, and the other portion of the soil the inorgan- 
ic matter. The quantity of organic matter va- 1 
ries very much — in some soils it exists to the 
extent of two per cent., in others 15 and 20 per 
cent., and in peaty soils sometimes as high as 
70 per cent. If you take a piece of vegetable 
matter and burn it, such as this wood, you will j 
find here, also, that a large portion will not burn | 
away, but remains, forming wood-ash. It is 
the same, then, with regard to the plant as to 
soil — a part burns away and a part remains. 
If you look at the tables yju will see that dif- 
ferent plants have different proportions of inor- 
genic matter — thus, meadow hay leaves nine or 
ten percent, of incombustible matter. 
Again, ns to the animal sub-tances, take a 
piece of muscle, dry and burn it, and you shall 
find that the greater part of it will burn away, 
which is the organic matter, the remainder be- 
ing, as in the soil, and in the plant, the inorgan- 
ic and incombustible matter. Now, one hun- 
dred pounds of fresh muscles contain phos- 
phate of lime and other saline substances to the 
extent of one per cent, of incombustible matter. 
Thus, the three different substances, soil, vege- 
table and animal matter, consist of organic and 
inorganic matter ; but there is this difference, 
that in the soil there is a larger portion of inor- 
ganic matter than in plants and animals — in the 
latter, the greater portion burns away. 
I call your attention now to the inorganic por- 
tion of soil. By looking at the table you will 
observe that the inorganic matter consists ol 
different substances, such as silica, which forms 
a very large proportion of flint ; alumina, a sub- 
stance which forms a large proportion of pipe- 
clay; oxide of iron, which is the rust of iron ; 
potash, of which the potash you get Irom the 
shops mav serve to give you an idea ; chlorine, 
which is a kind of air; and then there is manga- 
nese, phosphoric acid, and carbonic acid. 
These substances are fiuind in all soils, but not 
in equal proportions. You will see in the ta- 
ble before you the details of the constitution of 
a soil which would yield good crops for perhaps 
a hundred years. Were you to possess such a 
rich soil as that, and such soils are to be got in 
the virgin land at the Cape of Good Hope, on 
the banks of the Ganges and the Mississippi, 
you would always find that it would contain a 
notable quantity of all these different elements. 
In the second column of the table you have a 
list of the quantities of the different substances 
of a soil capable of yielding good crops, but 
which would require to be regularly manured. 
You will observe that opposite three ot the sub- 
stances the word “trace” is put, which means, 
that though the substance was not absent alto- 
gether, yet It existed in so small a quantity that 
it could not be weighed. In the rich virgin soil 
stated first, vou observe that there is of lime 59 
percent., while in the second column there is 
only 19. Of phosphoric acid there is four in 
the one, and only two in the other. In the third 
column of the table is the constitution of a soil 
so barren, that though manured, it could not 
produce a good crop. You see that there is a 
great manv gaps in the list; in short, there is 
only five substances which exist in anything 
like quantity. 
So much for the substances which exist in 
all good soils ; and you may be sure that it any 
soil does not produce a good crop, some one or 
other of these substances are wanting. The 
question then arises, how do soils come to have 
such different compositions as these? I stated 
to you how the crumbling down of rocks formed 
the soil along with the accumulation of organic 
matter in it ; and if I had had time, I would have 
directed you to a geological map, and shown 
that in everv country the rock on which the soil 
rests is different; and if it be true that the crum- 
blingdown of rocks forms the soil, you learn at 
once how soils must differ very much in their 
composition. In feldspar soils, of which rocks 
principally consist, you will observe only silica, 
alumina and a few others. A soil formed from 
this must therefore contain a large quantity of 
these substances which are on all soils, while 
it would be deficient in many others. As soils 
differ in this way we are led to this practical 
question — how can we make this soil to be like 
that soil, or how can a bad soil be made equal 
to a good one ? The answer is simply, that you 
must supply those substances which are want- 
ing in the soil — you must supply as much pot- 
ash or lime as are wanting in the third or poor 
soil, and as much lime and phosphoric acid as 
is wanting in the second, to make up all the 
constituent elements which exist in the first or 
rich virgin soil, and which are necessary to en- 
able the soil to produce a good and profitable 
crop. This shows you the benefit ot an analy- 
sis of the soil, by which a farmer is enabled to 
decide what the soil requires, and proceed ac- 
cordingly, 
I shall n°xt speak ot vegetable substances ; 
and first, as to the inorganic part of them. If 
you take the ash which remains behind, when a 
plant has been exposed to the fire, andanalyze 
it in the same way as with the soil, you will 
come to this result, that the inorganic part of 
the plant contains precisely the same substances 
fsthe inorganic portion of the soil. In the ta- 
ble on my right hand, you see the composition of 
a lOOO pounds of hay. The different kinds of 
hay have different quantities of the same sub- 
stance, w hich substance is the same as in the 
soil. In reference to the ash of vegetables, 100 
lbs. of wood would leave behind not more than 
a hall a pound of ash. Perhaps you may be 
inclined to ask why, seeing that out of 100 lbs. 
one half pound only is ash, can that half pound 
be necessary for the existence of the plant, or 
is it rather merely accidental, and in no respect 
making any difference to the plant? No such 
thing, gentlemen. That half pound of ash is 
just as much an essential part of the plant as the 
99^ lbs. which burned away. Th'= same is the 
case with wheat, which leaves 2 lbs. of ash. I 
state these facts in order to bring you along with 
me in my exposition of the principles of the 
science, that you may see how I come to the 
conclusion, and which must be true, that the 
plant coul l not live— that it could not fulfil the 
purposes of nature, unless it contained this 
small quantity of inorganic matter. If you 
look to the table on the ash ot hay, you will find, 
there is an analogy between it and the soil. 
Red clovpr contains in one thousand pounds 
thirty-one pounds of potash; rye grass as little 
as nine pounds. Of phosphoric acid, rye grass 
contains one-third of a pound, red clover less 
than 7 lbs,, white contains five, and lucerne 13 
lbs. We learn, then, that these substances are 
present in different proportions in the ash of dif- 
ferent kinds of hay, and from that we draw se- 
veral important practical deductions. Let us 
inquire whence do the plants derive the organic 
and inorganic parts of which they consist. 
They derive the organic partly from the soil and 
partly trom the air; the inorganic solely from 
the soil. In the air float certain proportions of 
all those substances which enter into the organ- 
ic part, but none of those which enter into the 
inorganic part of the plant. Now, the different 
kinds of plants in the soil will materially affect 
its constitution, and have a remarkable influ- 
ence upon that constitution. Suppose I grow 
lucerne upon the very fertile soil detailed in the 
table: as 'lie lucerne takes out a large quantity 
of lime and of phosphoric acid, you will see 
that the crop would rob the soil of a large pro- 
portion ol lime and of phosphoric acid, and that 
therefore it would not grow the same crop with 
'hat luxuriance which characterised it at fi'si, 
because it could not supply with the same ease 
and abundance those peculiar substances upjn 
