Agriculture.—On Spring Pasture. 355 
ole one, from a weaker, arsenical solution. Coffee was then 
added to the solution of copper and of carbonate of potash, 
but withowt arsenic, and the effect resembled that of the 
stronger arsenical solution, more than this last was resembled 
by that of the weaker. 
But the most important facts ——— by Dr. Porter 
remain still to be stated. He found, that,—in the production 
of Scheele’s green, by arsenic, sulphate of copper and car- 
bonate of potash,—chromate of potash might be substituted 
for the arsenic; and that it produced a precipitate not to be 
distinguished, by the eye, from Scheele’s green. He ascer- 
tained, also, that even Mr. Hume’s celebrated test, nitrate 
of silver, (as modified in its application by Dr. Marcet,) 
gave, with chromate of potash, a sano Peariplinies which, 
when placed side by side with one produced by arsenic, 
could not be distinguished by their pos and sspcamaiie 
Dr. Porter’s experiments appear, then, to throw sull greater 
suspicion on the infallibility of tests ‘for arsenic, and are 
worthy of being repeated.* His results were exhibited to us. 
The nitrate of silver used by. Dr. Porter, was the lunar caustic dissolved, 
a the chromate of potash 
Boe wigs ears a mf  . 
ae - bz 
ae pe, Sera Ag at = Eee ae z Ms ei oe a re = 2, We 6 Bsa cf S. Pua bg 
sain XIX.—On Spring 4 Pasture ; by Professor Ext Ives. 
«A roaws whieh wil gay i in the autumn, of a size suf- 
equally unfavourable to vegetation. All the grasses occa- 
sionally, and at least the s folnee e and the roots of many, are 
destroyed by the si f the winter and spring. — 
7 the 5 wuees jit requires the whole of the pfevions sum- 
