GLEANINGS IN BOTANY. 
339 
Dissolve the iodide of potassium in 10 ounces of distilled water, and, having 
made the solution warm, add the corrosive sublimate, previously dissolved in 
a littie water, gradually, until the red precipitate, which is thrown down, begins 
to be formed permanently. Next dissolve the potash in about its own weight 
of water, and add it gradually to the mercurial solution, with constant stirring. 
Lastly, add sufficient distilled water to make the liquid measure a quart, and 
set it aside that it may become clear. In the course of about twenty-four hours 
the cloudiness will have disappeared, and the liquid may be decanted from the 
deposit.* 
In order to employ the test quantitatively, it will be necessary to prepare a 
solution of ammonia of known strength, with which the reactions obtained with 
the several distillates can be compared. For this purpose 315 grains of sal- 
ammoniac are dissolved in 10,000 grains of water. Such a solution contains one 
ten-thousandth of a grain of ammonia, NH g , in each grain of the liquid. 
Five ounces of the distillate are now mixed in a tall glass cylinder with 50 
grains of the mercurial solution, measured by a pipette: if ammonia is present, 
a yellowish colour will be developed of greater or less intensity ; though, of 
course, no change will be observed should ammonia be absent. The liquid will 
remain clear if the ammonia do not exceed grain in the five ounces. 
To estimate, in such a case, the quantity of ammonia, place in a similar glass 
cylinder 50 grains of the standard sal-ammoniac solution, dilute it with five 
ounces of distilled water previously ascertained to be free from ammonia, and 
add to it 50 grains of the mercurial test solution. If the tint coincides in in¬ 
tensity with that furnished by the distillate, which has received an equal quantity 
of the mercurial test, the amount of ammonia may be considered to correspond 
with that taken in the liquid for comparison. 
If the distillate appears to have a deeper or a paler tint, a second approxi¬ 
mative trial with a larger or smaller quantity of sal-ammoniac must be made, 
and so on, till rhe operator is satisfied that the tints coincide. In general it will 
be possible to make a guess; founded upon experience, at first sight of the re¬ 
action obtained with the distillate ; so that it will seldom be necessary to make 
many trials with the standard solution. 
When the quantity of ammonia exceeds the grain per gallon, it is neces¬ 
sary to determine the amount by neutralization. 
A test acid containing 2 882 grains of oil of vitriol in 1000 of water will con¬ 
tain such an amount of acid that 1 grain will neutralize one ten-thousandth of 
a grain of ammonia. The neutralization is effected in the ordinary way, using 
infusion of litmus to indicate the point of transition from alkalinity to com¬ 
mencing acidity. Mr. Chapman states that a better estimate may be made by 
diluting, and then applying the Nessler test than by titrating with a standard 
acid. 
GLEANINGS FROM BRITISH AND FOREIGN JOURNALS IN 
BOTANY. 
Irritability of Plants. 
We have undertaken during the present year, a number of experiments 
on the irritability of plants, which show that the faculty which some of them, 
and especially the Sensitive Plant, possess of executing movements which appear 
voluntary, may be suspended by many agents, such as ether, chloroform, carbonic 
* The Nessler test may be made, if desired, by using 50 grammes iodide of potassium and 
120 grm. of potash made up with water to 1 litre. The pipette used for measuring should 
deliver 11 cub. cent. 
