Improvements in the Purification of Chloroform.
Year: 1891

page_text: Date of Application, 12th Sept., 1891-Accepted, 17th Oct., 1891
COMPLETE SPECIFICATION.
Improvements in the Purification of Chloroform.
I, SYDNEY PITT, of Sutton, in the County of Surrey, Gentleman, (a communi-
cation to me from abroad by Raoul Pictet & Co., of No. 28 Usedom Strasse,
Berlin, in the Empire of Germany,) do hereby declare the nature of this invention
and in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement :---
Chloroform is a product of great importance in industry and medicine. It is
desirable for many reasons to obtain it perfectly pure.
In practice chloroform is made in three ways:-
1. The reaction of chloride of lime on diluted ethylic alcohol gives by distillation
chloroform.
2. Chloride of lime when allowed to react on acetone produces chloroform.
3. Chloral hydrate is decomposed by an alkali and chloroform is distilled from
the liquor.
Now these three processes however carried out always allow impurities to pass
into the liquid chloroform obtained by distillation.
The alcohols employed contain a series of essential oils, various alcohols,
amylic, methylic &c. &c. These foreign products disturb the chemical reactions
and cause a part of these impurities to pass into the condensed vapour with the
chloroform. Subsequent washings of the chloroform are unable to separate these
bodies which are intimately mixed with the mass.
The acetones are as impure as the alcohols and everything said above of
chloroform from alcohol is applicable to chloroform from acetone.
Chloroform from chloral is more pure than the preceding but the vapour from
chloral hydrate separates with difficulty from the vapour of chloroform and it is
impossible to preserve the chloroform from traces of this body, the specific action
of which is very characteristic.
Again the chloroform when obtained is directly mixed with one per cent. of
alcohol to give it relative stability.
Light, and certain chemical and physical agents tend in a manner at present
imperfectly understood to decompose chloroform and to produce in the midst of
the liquid secondary products in which hydrochloric acid and free chlorine are
found.
If these two substances namely hydrochloric acid and chlorine are neutralized by
the addition of bases such as soda and by the iodides there nevertheless remains in
the chloroform thus treated a series of heterogenous bodies consisting essentially
of the series of the tetrachlorides of carbon which remain dissolved in the liquor and
no reagent known at present can discover or eliminate them.
The object of the present invention is to purify in a methodical and complete
manner chloroform made by one or other of the three above described methods
and to give to industry and medicine a chemically pure chloroform.
The process of purification is divided into three distinct steps.
1st step. Ordinary chloroform is introduced into a jacketted vessel represented
in the annexed drawing.
A cylinder of copper or other metal A is surrounded by a jacket B forming a
second cylinder hermetically soldered at top and bottom to the cylinder A.
Between the two cylinders an annular space of about 20 to 40 millimetres is
left for the purpose of containing a volatile liquid capable of producing very
great cold.
Pictet's liquid, chloride of ethyl, methylic ether, ammonia, carbonic acid,
protoxide of nitrogen and ethyline may be selected at pleasure as the liquid.

page_text: The volatile liquid is introduced by the orifice D and the vapours are sucked
out by a pump connected to the orifice I. The vapour may also be allowed to
escape directly to the air by the orifice I or into a gasométer to prevent it being
lost.
After having introduced ordinary chloroform into the interior of the cylinder A
the selected volatile luid is allowed to flow in at the orifice D.
The vapour which spontaneously forms in the jacket B at once lowers the
temperature of the chloroform and allows its temperature to be brought down to
82° Centigrade.
-
80° to
-
The result is that either by means of a pump drawing the vapour from the
Pictet's liquid &c. or by allowing to escape directly into the air or into a
gasometer under atmospheric pressure the vapours of protoxide of nitrogen or of
ethyline the temperature of-82° may be obtained throughout the mass of chloroform:
To prevent the volatile liquid from being drawn out an intermediate receiver C is
provided on the exit vapour pipe which plays the part of a vapour dome.
When the whole mass of chloroform is cooled to from -80° to - 82° it is found
that the chloroform has become completely milk like and that a multitude of
greeny-white flakes are floating in the body and at the surface of the liquid.
The low temperature has transformed into solid bodies a number of substances:
foreign to the chloroform-water, hydrated alcohol, various coloring matters..
The chloroform is then filtered by opening the cock E at the bottom of the
apparatus above which is placed upon a grating on the upper surface of the
bottom a filtering substance such as filtering paper, cotton, fine fabric &c. &c.
The chloroform which runs out at the cock E is absolutely transparent and
without colour.
The chloroform so purified still contains impurities and the second step advances:
the process of refining.
2nd Step. The same jacketted vessel A is employed for the second operation
after it has been perfectly cleaned and after the filtering substance F, which is
charged with the deposits of the first filtering operation, has been changed. The
chloroform already improved by the first step is re-introduced into A and the
temperature is reduced this time to below 80° causing the chloroform to freeze
-
and crystallize against the sides of the reservoir.
When three quarters of the mass has crystallized the cock E is opened and-the-
liquid non-crystallized part is allowed to run out into a special reservoir.
On' stopping the pump the temperature rises rapidly and the crystals of
chloroform melt.
The liquid thus obtained is filtered and is run out of the cock E into the
reservoir provided for good products.
The chloroform has now arrived at the degree of absolute purity that it is
desired to attain, except that in consequence of the somewhat prolonged stay in.
the metal apparatus and of the filtering substances employed it is possible that
traces of foreign matters and dust still remain in suspension.
We now come to the third step:-
3rd Step. The third step consists in distilling the chloroform furnished by the.
second step at a very low temperature under the influence of a sufficient vacuum.
The vapour of the purified chloroform is brought from the special reservoir which
contains-it into the cold vessel A by the upper opening 'H.
By means of an air pump and of the pipe K a vacuum is made in the vessel-A
which communicates freely by the opening H with the reservoir containing the
chloroform. The vapour is thus condensed against the cold sides of the vessel A-
and the liquid thus obtained by distillation is absolutely freed from dust andțall
foreign bodies of whatever nature. Care should be taken in this third-operation!
to separate the products of rectification into three parts, the head products, the.
middle and the tail.
80 per cent. of the total product may be taken as the middle and a. medicinal
product is thus obtained which is chemically pure.

page_text: It is unnecessary to state that the apparatus shown diagrammatically in the
drawing may be modified in any suitable manner and that the invention is not
limited to the employment of any particular form of apparatus.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is :-
-
The process of purifying ordinary commercial chloroform which consists in :-
1. Solidifying tue foreign bodies crystallisable before the temperature reaches
- 80° and in filtering the cold liquid mass.
2. Crystallising the chloroform itself and eliminating from it the final non-
crystallisable part which contains the impurities.
3. Distilling the chloroform thus obtained at a very low temperature and
collecting the middle products.
10 tambay 1001
CARPMAEL & Co.,
Agents.