US2178486A - Device for signaling the presence of illuminating gas in inhabited premises - Google Patents

Description

Oct. 31, 1939. G. MENOZZI 2,178.486

DEVICE FOR SIGNALING THE PRESENCE OF ILLUMINATING GAS IN INHABI'I'ED PREMISES Filed Aug. 29, 1956 Fz'y/ UNITED STATES PATENT OFFICE DEVICE FOR SIGNALING THE PRESENCE OF ILLUMINATING GAS 1N INHABITED PREM- ISIS Giuseppe Menozzi, Messina, Italy Application August 29, 1936, Serial No. 98,613 In Italy December 19, 1935 1 Claim.

It is known that there are devices for signaling the presence of illuminating gas in inhabited premises founded on the attribute of platinum sponge of becoming heated in the presence of hy- 5 drogen and oxygen.

Generally, these devices consist of an ordinary mercury thermometer with an electric contact whose bulb is in contact with a platinum sponge; the heating of the sponge caused by the gas diffused in the room, in consequence of eventual escapes, causes the mercury in the thermometric column to rise until it establishes an electric contact, thus provoking the closing of the alarm circuit. In other devices, instead, the ordinary mercury thermometer is substituted by a type of differential thermometer, actuated by gas or by electric contact, having one of its bulbs in contact with a platinum sponge. None of the preceding devices, however, as far as is known, appears to be made according to experimental data regarding the rising of temperature to which a piece of platinum sponge might be subject in premises in which an escape of gas occurs. This means, consequently, that in none of the said devices such working conditions occur, and that no device of the kind, as far as the applicant is aware, has been practically realized.

The present invention is based on an experimental research aiming at establishing the conditions for the heating of 'a platinum sponge, or other catalyzer of the kind, placed .in a room in which there occurs an escape of gas.

This research gives the following result:

As the ordinary illuminating gas consists essentiallyof a combination of hydrogen and oxide of carbon and that the heating of the platinum sponge is due to the reaction 2H2+Oz=2H2O, it follows-that in ordinary dwellings the platinum sponge coming into contact with escaping gas gets 40 heated by only a few degrees (not more than about ten) independently of the position which it occupies in the room, even when there occurs a considerable escape of gas, and this because the hydrogen contained in the gas, owing to its very high coeflicient of diffusion spreads rapidly all over theroom (and does not gather under the ceiling of the room, as some people erroneously believe) and also out of the room through the inevitable fissures of the doors and windows, reaching, however, in the room a concentration limit given by the equilibrium which depends, besides on the entity of the escape, on the size of the room, and on the number and conditions of the doors and windows. In consequence of this, several hours after the gas escape has occurred, the concentration of the hydrogen is the same as that attained shortly after the beginning of the escape; while the concentration of the oxide of carbonium (which is the poisonous constituent of the gas) increases continuously as time passes by ii because, having a density equal to that of the air.

it spreads very slowly.

This is the reason why the devices already known do not attain the desired object. In fact: in the case of devices containing ordinary mer- 10 cury thermometers, it happens that as the latter are influenced by the variations of the temperature in the room, which may even rise to 30 degrees centigrade and upwards (taking into ac count the fact that during the winter the tem- 15 perature may fall considerably in the hours of the night, which are the more dangerous ones, compared with the maximum reached during the summer), it follows that for the functioning of the device in these conditions the platinum 20 sponge must produce in the bulb of the thermometer a heat of over 30 degrees centigrade in order to ensure such functioning at any hour during the day and night.

As regards devices provided with a differential 25 thermometer the failure in functioning is due to the lack of knowledge of the low concentration limit attained by the hydrogen and, consequently, to the lack of knowledge of the maximum temperature which the platinum sponge may reach 30 in a room in which occurs an escape of gas. Consequently, in planning the differential thermometers used in the devices already known, no account is taken of the minimum sensitiveness required for their working. 35

Object of the present invention is to provide a device of a suff cient sensitiveness as will ensure the working of the alarm device in any dwelling room. To obtain this, it is assumed that the M heating of the platinum sponge may be reduced to only 3 degrees centigrade" in very large rooms with numerous apertures so that the signaling device is constituted of a differential thermometer worked by gas with electric contact capable of closing an electric circuit whenever between its two bulbs there occurs a difference of temperature of 3 degrees centigrade, or more. a

In practice, with this device, in one room measuring meters 3 x 3 x 3, the closing of the 5g circuit occurs after a couple of minutes.

In the annexed drawing are illustrated, only by way of example and without limitation, two manners of realization of the thermometers and of the device referred to in the invention. so

Fig. 1 is an elevation of a thermometer used in one embodiment of the invention.

Fig. 2 is a view. somewhat diagrammatic, of one embodiment of the invention complete, the bulb covers being shown in section.

Fig. 3 is an elevation 01' another embodiment, the bulb covers being shown in section.

A thermometer oi the kind (Fig. 1) is made of two glass bulbs A and B connected by means of a capillary tube C with two bubbles l and 2, in which is contained a drop of mercury 3.

Inbubbles I and 2 are soldered two platinum threads 4 and 5, of which one 5 is in permanent contact with mercury 3; the other is meant to come into contact with the mercury only in consequence of the heating of bulb B. The two bulbs A and B contain air, or preferably hydrogen under ordinary, or higher, pressure. When the two bulbs are at the same temperature, the mercury assumes in the capillary tube the position shown in the drawing (Fig. 1) and must retain it whatever be the temperature of the room, provided it be the same in the two bulbs. If bulb B gets heated, the pressure of the gas contained therein increases thus provoking a displacement of the mercury towards bulb A until the restoration of an equal pressure in the two bulbs.

The contact between the mercury and platinum thread 4 of bubble I may be fixed in advance for a determined excess of temperature of bulb B respect to bulb A. When an equal temperature has been re-established in the two bulbs, the mercury will resume its primitive position.

The essential characteristics of this thermometer are therefore:

(1) Absolute indifference to the variations of the temperature of the room.

(2) Closing of the electric contact whenever the temperature of one of the bulbs exceeds by a number of degrees fixed in advance the temperature of the other bulb, whatever the temperature of the latter may be.

(3) Possibility of fixing this number of degrees as small as may be desired, the only obstacle to the moving of the drop of mercury being reduced to the sole attrition with the casing and with the platinum thread 5.

Fig. 2 shows a form of execution of the device referred to in the invention. A and B are the two bulbs of the thermometer; 'l is the catalyzer of the reaction between hydrogen and oxygen in the shape of a small cylinder in contact with bulb B; 6 is a small cylinder of the same dimensions as I but made of a substance having the same thermic conductiveness of small cylinder 1 but without having the same catalytic properties; so that, in default of a gas escape, the variations in the temperature of the room have the same influence in the two bulbs A and B. P are the batteries and C an alarm bell. (Other accessories, such as an automatic apparatus for closing the gas tap, or other signaling means may be added in the manner already known.)

When, owing to an escape of gas, hydrogen comes into contact with platinum sponge I, the latter gets heated by a certain number of degrees though the concentration of the hydrogen be very low, and being in contact with bulb B of the thermometer, it communicates such rise of temperature to the gas contained therein, which dilates pressing the mercury in the capillary tube so as to close the electric circuit which actuates the alarm signal, or the protective apparatuses installed.

The thermometer is made in such a way (volume of the bulbs, diameter of the capillary tube, distance of the drop of mercury from platinum thread 4, thickness and quality oi the glass, etc.) that the closing of the electric circuit happens when the temperature of bulb B is by only 3 degrees centigrade superior to that of bulb A; which, in a room of the size 01 meters 3 x 3 x 3 and with three windows and adoor, (closed at the time of the experiment), occurs after one minute from the complete opening of a common gas tap.

An improvement of this thermometer is represented in Fig. 3. In this thermometer the two bubbles i and 2 of Fig. 1 have been suppressed; the platinum threads of a sufliciently reduced thickness have been both placed on the same part and introduced into the capillary tube without any contact between each other and with their points on the same plane. The mercury drop has been reduced to two or three millimeters in length.

By this modification there has been obtained an increase of sensitiveness in relation to the form represented in Fig. 1, as the resistance opposed to the motion of the drop of mercury has been considerably reduced. Furthermore, the presence of platinum threads of a small thickness ensures the following result: when, in consequence of the heating of bulb B, the mercury comes into contact with the two platinum threads causing the closing of the alarm circuit, an electric current originates through the said threads which, being of a small diameter opportunely chosen (about millimeter 0.1), get heated and consequently cause the heating of the gas of bulb A up to its reaching a temperature above that of the gas of bulb B. In consequence thereof, the

drop of mercury is repelled and determines the interruption of the circuit, to resume once more contact with the platinum threads when, following upon a natural cooling down, the temperature of the gas in bulb A has become inferior to that of bulb B; and so on until there remains in the room the presence of the illuminating gas. Thus the intermitting closing of the alarm circuit is obtained.

This intermittent closing does not impair anyhow the advantages of the device, because the action of the automatic apparatuses eventually introduced in respect of the alarm bell, closing of the gas tap, lighting of the apartment, etc. is ensured by means of a relay operated by the first closing of the circuit. The intermittent closing ensures furthermore the return to its place of the drop of mercury when the presence of gas in the room ceases, and at the same time prevents that, in consequence of an eventual excessive heating of bulb B, the drop of mercury be projected into bulb A.

The device thus constituted is wrapped in a layer of cotton-wool, or of glass-wool which, besides ensuring its regular working, preserves it from dust and froni the dampness of the atmosphere. The whole is then properly closed in a metallic net placed on an insulating base.

Another improvement of the differential thermometer aforedescribed, as regards promptitude and sensitiveness, is obtained by substituting the two glass bulbs A and B with two bulbs made of thin silver plate.

What I claim and desire to secure by Letters Patent is:

A device for signaling the presence of illuminating gas in inhabited premises, comprising two axially aligned gas filled bulbs, a straight line capillary tube connecting said bulbs along their axes, a drop of mercury in said tube normally balanced as to position by equal gas pressure in the two bulbs when both bulbs are at the same temperature, each-bulb being covered in like degree by covers having the same thermic conductivity, one of said covers having catalytic properties in excess of the other, and electric terminal wires projected into said capillary tube to cooperate with said mercury drop for the purpose of closing an electric circuit upon a determined rise in the temperature of the bulb having the catalyzer above that of the surrounding atmosphere, said wires entering said capillary tube at one end and both wires being normally out of contact with said mercury drop for purposes described.

GIUSEPJPE MENOZZI.

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