APPARATUS FOR PREPARING NITROUS OXIDE GAS. 
63 
to the notice of chemists and dentists the result of my experience in the form of 
the following directions:— 
In preparing nitrous oxide from comparatively pure nitrate of ammonia there 
are three important points to be observed, viz. 
First. To keep the temperature steady, such as will decompose the salt into 
water and nitrous oxide only. 
Secondly. To free the gas from impurities by well washing through proper 
solutions, and 
Thirdly. To be careful in expelling the air from the flask and wash bottles 
before collecting the gas. 
The necessary articles are— 
Pure nitrate of ammonia. 
A good Bohemian glass flask of suitable size and shape. 
Four wash-bottles and tubing. 
Water and solutions of caustic potash, and protosulphate of iron. 
And lastly a lamp (gas or otherwise) having some appliance that will regu¬ 
late the heat in proportion to the rate at which the gas is liberated. 
Nitrate of ammonia is made almost entirely by neutralizing pure carbonate 
of ammonia with pure nitric acid, and in this way a pure and comparatively 
cheap article is obtained. If, however, the ammonia contains any chlorides, or 
the nitric acid traces of sulphuric or hydrochloric acids, the salt will contain 
chlorides and sulphates, and when heated will give off chlorine and nitric oxide 
gases. These are the only impurities that occur, so that a salt containing 
neither of these may invariably be considered pure. 
The apparatus that by experience I found most convenient consists of a flask 
(A), see diagram, of about 60 oz. capacity, having a wide mouth (1£ inch inside) 
to facilitate the introduction of the salt, and fitted with a large cork carrying a 
glass tube f inch wide. This flask is suspended by a chain or wire fixed to the lip 
from a bracket or hook, as may be convenient, over the naked flame of a Bunsen’s 
burner. A long bent tube (B) connects the flask with the first bottle (C), which is 
not a wash-bottle, but simply a receiver for the condensed water from the nitrate, 
a means of communication to the thermal moderator, through which (when 
the flask cools at the end of the process) the air passes to supply the vacuum. 
This bottle has three openings, one Tor the tube from the flask, another con¬ 
nected with the first wash-bottle, which is of the same size as the receiver, viz. 
40 oz., and is constructed as au ordinary wash-bottle, containing 16 oz. water. 
The exit tube of this bottle is connected to a second bottle, containing a solu¬ 
tion of protosulphate of iron (1 to 7), and this to a third containing 16 oz. solu¬ 
tion of caustic potash (consisting of 8 oz. liq. pot. and 8 oz. water). The third 
tube of the bottle (C) is in communication by means of an india-rubber tube 
with the thermal moderator. This latter is a bottle (D) with three perforations, 
—two at the top, and one near the bottom. One of the perforations in the top 
contains a tube through which passes the pressure from the first bottle (C) and 
flask (A); and the other top perforation has a perpendicular tube (E) fitted up 
with a whistle at least six inches above the column of the water under the 
greatest pressure, the other end passing midway into the water. The third 
perforation, near the base of the bottle, is provided with a tube (F) that is suffi¬ 
ciently widened a little above the ordinary level of the water to carry a float 
(/). The float is attached by means of a cord to the end of a lever (Gf, H). 
This lever has for its fulcrum (H) the plug of the gas-tap that supplies the heat 
to the flask, and at the other end of the lever a counterpoise (I), so that when 
the weight of the float is supported by the water instead of the arm of the 
lever, the counterpoise will weigh down that end, and so alter the position of 
the tap (H), or, in other words, turn off the supply of heat. 
The principle of this apparatus is based upon the fact that pressure exerted 
