ation to, 84.

Pliny, on lime as a manure, 449;
on salt as a manure, 465.

Pockets a source of phosphoric acid, 202.

Poisons, effect of, on nitrifying organisms, 176.

Polstorff on ash constituents of plants, 53.

Polyhallite, potash in, 220, 420.

Porphyry, in guano, 303;
phosphoric acid in, 202, 211.

Potash, 212-220, 418-423;
in ash of plants, 54;
in barilla, 420;
chloride of, 218;
condition of, in soil, 216;
in cows' excrements, 280;
in drainage-waters, 217;
in farmyard manure, 260;
in felspars, 220;
in fleece, 217;
fixed by soils, 58;
importance of, in soil, 88;
in kelp, 420;
less important than phosphoric acid, 212;
manures, 218, 418-423;
muriate of, 218, 421;
necessary for nitrification, 171;
necessary for plant-growth, 55;
occurrence of, 213;
in ocean, 213;
in oxen excrements, 280;
in pig excrements, 280;
in plants, 216;
position of, in agriculture, 212-220;
relative manurial value of, 556;
Scottish soils supplied with, 419;
in sheep excrements, 280;
soda replaces, 466;
sources of loss of, 217;
in Stassfurt salts, 214;
statement of, in analyses of manures, 542;
in sugar-beet refuse, 219;
sulphate of, 218, 421;
in wood-ashes, 218, 220, 419.

Potash manures, 218, 418-423;
application of, 422, 480
--rate of, 423;
barilla as, 420;
crops suited for, 423;
relative importance of, 418;
soils suited for, 423;
sources of, 419;
Stassfurt salts as, 420;
wood-ashes a source of, 419.

Potassium phosphate in concretionary nodules, 328.

Potassium sulphate, in Chincha guano, 305;
in concretionary nodules, 328.

Potatoes, effect of farmyard manure on, 520;
fertilising ingredients removed from soil by, 485;
grown with covered manure, 289;
Highland Society's experiments on, 518;
manurial constituents in, 282;
manuring of, 517-522
--in Jersey, 529
--influences composition of, 521;
potash removed in, 217;
Rothamsted experiments on, 519, 571.

Precipitated ammonium phosphate in concretionary nodules, 328.

Precipitated phosphate, 330, 387.

Precipitation, treatment of sewage by, 436.

Priestley, discovery of evolution of oxygen by plants, 11;
on nitrogen in plants, 40.

Prussiate of potash, manufacture of, 353.

Pugh on sources of plant-nitrogen, 42.

Punta de Lobos guano, 302;
nitrogen in,