Actinometer and Method of Measuring the Chemical Effect of Light.
Year: 1893

page_text: COMPLETE SPECIFICATION.
Actinometer and Method of Measuring the Chemical Effect of Light.
I, JOSEF KREMER, Photographer, of M. Gladbach, in the Kingdom of Prussia,
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:
This invention is based on the fact, that a mixture of hydrogen and chlorine
will remain unaltered in the dark, but will form hydrochloric acid and reduce
its volume, when exposed to daylight.
On the other hand, if a pair of electrodes be dipped into hydrochloric acid,
and an electric current caused to pass through the same, the acid is decomposed
into its elements, hydrogen being given off at the negative pole and chlorine at
the positive pole.
If the decomposition takes place in a receptacle filled with hydrochloric acid
and provided with a narrow open prolongation or neck, the gas bubbles collect
above the hydrochloric acid and the latter is driven towards the outlet. If this
takes place in the dark, the gaseous mixture remains unaltered, but as soon as
daylight falls on the gaseous mixture, the chemical combination described above
takes place, and also the reduction of volume which results therefrom, in
consequence of which the hydrochloric acid previously driven out flows back into
the space filled with gas. In strong light this process goes on rapidly and in weak
light slowly.
According to the length of time during which the light falls on this gas mixture,
the volume of the gas mixture will be reduced more or less, and a larger or
smaller quantity of hydrochloric acid will be allowed to flow back into the gas
space.
In the accompanying drawings:
Fig. 1 is a side view, Fig. 2 a plan and Fig. 3 a vertical section of an instrument
embodying my invention.
Fig. 5 is a horizontal section through the electrodes.
Fig. 4 represents the apparatus in operation.
The instrument chiefly comprises a glass vessel a and a vertical tube b com-
municating with the same.
On this tube is mounted a moveable graduated scale.
The vessel and the lower part of the tube is surrounded with a jacket or casing
which is impervious to light, and provided above the vessel a with a flap k. The
latter covers an opening, through which the light may act upon the vessel, when
desired. Into the vessel a are fitted a pair of electrodes (as shown in Fig. 5)
connected with a constant galvanic battery or other suitable source of electricity.
If the electric circuit is closed, and thereby hydrochloric acid decomposed, the
gas bubbles resulting from the decomposition collect in the vessel and drive the
excess of hydrochloric acid in the tube b up to a certain height.
If now the flap k is raised, and light allowed to fall upon the glass vessel,
the gases combine gradually, to form hydrochloric acid, and the rapidity with which
this takes place corresponds to the actinic power of the light.
In consequence of this the hydrochloric acid in the tube b descends in proportion
to the actinic effect of the light, and the latter may therefore be measured on the
scale, which has been placed so, that its zero point coincides with the original level
of the liquid.
To avoid an excessive length of tube, a collecting bulb c may be inserted in the
same near its base.
This instrument is chiefly intended as an auxiliary in photographic copying, and

page_text: especially for those processes, in which the effect of the light cannot be recognized
without an instrument.
I would remark, that the use of this instrument is not necessarily restricted to
hydrochloric acid or to a mixture of hydrogen and chlorine gas, as there may be
other liquids or gases which possess the properties mentioned above.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is ;-
1. The method of measuring the actinic effect of light, which consists in
electrically decomposing hydrochloric acid contained in a closed vessel, sub-
sequently exposing the resulting gases to light and measuring by means of a
graduated scale the reduction of volume produced by the said exposure, substantially
as described.
2. An electro-chemical actinometer comprising a closed glass vessel connected
with a tube, and protected from the influence of light, an adjustable scale
adapted to indicate the level of liquid in the said tube, a pair of electrodes
placed in the said vessel and connected with a source of electric energy, and
means for admitting light to the contents of the said vessel, when required,
substantially as described.
Dated this 3rd day of August 1893.
FAIRFAX & WETTER,
433, Strand, London, Agents.