ME. W. CEOOKES OX THE ATOMIC WEIGHT OP THALLIUM. 
301 
or the bumping of the acicl in a will be very violent. If the exhaustion is such that 
the mercury in the gauge stands at about 15 inches, the oil of vitriol distils quietly from 
the bulb a to b without bumping; but if the exhaustion is raised to above 1G inches, the 
ebullition becomes percussive. When most of the acid has distilled over into b the 
source of heat is removed, the mercury in the pump is again allowed to run until a 
vacuum is produced, and the bulb b, containing pure distilled sulphuric acid, is sealed 
up and removed by the application of a blowpipe-flame to the contracted portions of 
the tubes h and i. 
Carbonic Acid. 
Calc-spar is dissolved in pure hydrochloric acid. An excess of the spar is added, and 
the solution warmed ; to it is added lime-water made from pure or nearly pure lime, 
until the solution is alkaline to test-paper. This solution is filtered, and after heating 
it to at least 160° F., precipitated with carbonate of ammonium*. The carbonate of 
calcium thus precipitated is thrown on a filter and well washed with pure water. Thus 
prepared, the carbonate of calcium is a dense powder and perfectly pure ; or, if it con- 
tain any impurity, it will be a trace of carbonate of barium or strontium, which in no 
way interferes with its use in preparing carbonic acid. 
The dense granular carbonate of calcium is then strongly compressed in a steel 
diamond mortar into the form of coherent lumps. These lumps are introduced into a 
Woulfe’s bottle, and pure oil of vitriol poured over them. A continuous and not too 
rapid evolution of carbonic acid commences and is continued for some time. When the 
disengagement of gas becomes sluggish, a few drops of water restore the action. Large 
bottles must be used for this operation to avoid the inconvenience of the foaming to 
which the acid is liable. 
The carbonic acid is washed by passing through solution of sulphate of silver con- 
taining carbonate of silver in suspension to the consistency of thin cream, and it is then 
passed through a U-tube containing purified pumice-stone moistened with oil of vitriol. 
Ammonia. 
Ammonia is prepared in two ways : — 
1. Nitrate of potassium heated to incipient decomposition, and then crystallized three 
times from pure water, is dissolved to saturation in water, and put into a retort. 
Sodium amalgam containing about 1 per cent, of sodium is then added, and the whole 
| allowed to stand in a cool place for twelve hours. Gentle heat being now applied to 
I the retort, ammonia (from the reduction of the nitric acid) is driven over with the first 
* This precaution, which was first suggested hy Professor J. Lawrence, of Louisville, must not he over- 
looked, as it is desirable to obtain the precipitated carbonate of calcium as dense as possible. It the carbonate 
of ammonium he added to the cold solution, the precipitate, at first gelatinous, will ultimately become much 
more dense and settle readily ; the same is true if the mixture be heated after the addition of the carbonate 
of ammonium ; but in neither case will it be as dense as when the carbonate is added to the hot solution of 
chloride of calcium. 
2 s 
MDCCCLXXIII. 
