Improvements in the Production of Fluoroform.
Year: 1899

page_text: Date of Application, 6th Apr., 1893-Accepted, 17th June, 1899*
COMPLETE SPECIFICATION.
Improvements in the Production of Fluoroform.
I, FRIEDRICH VALENTINER, of the Firm of Valentiner and Schwarz, of Leipzig-
Plagwitz, in the Empire of Germany, Manufacturer, do hereby declare the nature
of the said invention and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:-
The only method mentioned in chemical technical literature for producing
fluoroform is that described by Meslans, and which is based upon the reaction of
fluoride of silver and iodoform in the presence of chloroform.
According to this method of Meslans, two parts each of iodoform and fluoride
of silver are brought into a small well-cooled retort with one part of chloroform
and slowly heated. The resulting fluoroform is led through a long leaden tube
cooled to 23° C., then over fluoride of silver at 100° C.: the fluoroform is collected
over mercury and freed from carbonic oxide by cuprous chloride and from chloro-
form vapor by dry caoutchouc.
This method of obtaining fluoroform, upon closer consideration, is found to
possess many drawbacks. The reaction between the fluoride of silver and iodoform,
when once set up, takes place rapidly, with development of strong heat, so that
the chloroform is rapidly vaporised and the iodoform is partly sublimed and
partly reduced to the state of decomposition products ranging down to free iodine
which render the product impure. With very small charges it is possible by
employing an inordinately large cooling surface, to retain the liquid and solid
decomposition products behind the cooling tube, which is surrounded with freezing
mixture, but the last traces of chloroform and fluoro-iodoform cannot be removed
even by subsequent agitation with dry caoutchouc. In the purification of the
fluoroform gas the enormous absorptive capacity of same for substances having
an odour, such as rubber, chloroform, fluoro-iodoform &c., constitutes a difficulty,
these substances being distinctly identifiable by their odour after careful purifi-
cation of the gas.
The present invention relates to a method of producing fluoroform on a large
scale. By this invention a slow and regular current of fluoroform gas can be
obtained which is completely free from impurities, so that no obstacle to the
general employment of fluoroform and utilization of its valuable specific properties
any longer exists.
The action can
The invention consists substantially in allowing fluoride of silver and iodoform
to react with each other in the presence of a suitable medium, the object of this
medium being to regulate the resulting current of fluoroform gas and to render it
possible for the operation to take place at a suitably low temperature in order to
avoid vaporisation of the iodoform, and in this way to obtain a product as pure
as possible. As such a medium there may be employed sand, powdered glass or
other similar substance having no direct part in the reaction.
be still increased if the evolution of the fluoroform be effected in the presence of
water, and in this case it is possible to so conduct the operation that chemically
pure fluoroform completely free from air is obtained. The water in this case serves
both as a sealing liquid and at the same time as cooling water for the reaction mix-
ture, so that overheating and consequent liberation of any decomposition products
which would render the fluoroform impure, is made impossible.

page_text: The employment of chloroform is altogether omitted according to the presen
invention.
The following examples will serve to illustrate the invention.
EXAMPLE 1.
1 kg. each of iodoform and fluoride of silver are intimately mixed with sand
then placed in a retort and warmed on the water bath. The reaction commences
at about 40° C. and continues quite gradually to the end, without necessity for
assistance by further supply of heat. The liberated fluoroform passes first through
a system of wash vessels containing alcohol, where it is freed from the odou
of iodoform and such like iodine compounds, and then, to free it from any carbonic
oxide it may contain, it is led to a second wash system filled with cuprous chloride
From this the fluoroform issues chemically pure and is collected over water. The
yield of pure fluoroform is almost quantitative. The advantages of this method
over Meslans' are obvious. The slow conversion of fluoride of silver and iodoform,
which can be regulated at will according to the proportion of the admixed sand,
entirely excludes bye-reactions, so that the transformation into fluoroform occurs
almost quantitatively. The small traces of impurities which adhere to the fluoro-
form as it leaves the vessel in which the reaction takes place are readily and com-
pletely removed in the wash vessels before mentioned, and the finished fluoroform
gas passes in an analytically pure state into the gasometer which is filled with water
as a sealing liquid.
EXAMPLE 2.
For the preparation of a chemically pure fluoroform free from air, the apparatus
shown in one convenient modification in the accompanying drawing may advan-
tageously be employed, the method of procedure being as follows;-
The generating receptacle A is filled to about half its height strata-wise with
alternate layers of iodoform and fluoride of silver, a layer of sand being interposed
between each. All air is then expelled by filling the receptacle up with water.
The cocks a and b are closed while the cock leading to the reservoir R is allowed
to remain open. As soon as the aqueous solution of fluoride of silver has pene-
trated through the sand to the first iodoform layer, the evolution of the fluoroform
begins. The gas collects in the upper part of the receptacle A and forces a corre-
sponding volume of water into the reservoir R. When the generating receptacle
has been thus placed under fluoroform gas to the required height, the reser-
voir R is shut off, the cock b is opened admitting the fluoroform to the wash
vessel B, which is completely filled with cuprous chloride solution, and finally the
gas is admitted by the cock c to the wash vessel C, which is filled with water
The wash vessels B and C are preferably each provided with water reservoirs R¹ R"
similar in object and arrangement to the reservoir R. Then the pipe connected
to the gasometer D, which pipe like all the other leading tubes is filled with water,
is opened, and the chemically pure fluoroform gas free from air is collected in the
gasometer.
The generation from the beginning to the end is regular and quiet and can be
regulated at will by mixing the iodoform with sand for the better penetration of
the aqueous solution of fluoride of silver. The water which is employed principally
as a sealing liquid in the generating container acts simultaneously as a cooling
medium for the reaction inixture, so that this process of production excludes all
overheating and consequently all impurities due to decomposition products.
The technical advantage of the method described lies in the direct obtainment of
chemically pure fluoroform free from air, and in the extremely simple manipula-
tion of the apparatus, which may be of any desired dimensions.
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:―
1. The method of producing fluoroform which consists in causing fluoride of

page_text: silver to react with iodoform in the presence of a medium such as sand, powdered
glass and the like having no part in the reaction, whereby the temperature is
regulated and a slow and regular current of fluoroform gas is liberated at a
suitably low temperature substantially as described.
2. The method of producing fluoroform which consists in warming an intimate
admixture of iodoform, fluoride of silver and sand, powdered glass or the like,
substantially as described in the first example herein given.
3. The method of producing fluoroform by the reaction specified in Claim 1,
which method consists in submitting fluoride of silver and iodoform together with
sand, powdered glass or the like, to the action of water, whereby the water dis-
solves the fluoride of silver and facilitates the action thereof upon the iodoform,
and at the same time serves as a sealing liquid and cooling medium for the reaction
mixture, a regular current of chemically pure fluoroform free from air being
obtained, substantially as described more particularly in the second example herein
given.
Dated this 6th day of Anvil 1900
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London,
Chartered Patent Agents.