The French Tissot Apparatus was the first gas mask to incorporate the "Tissot Principle" - This works by directing the incoming air from the filter around the eyepieces with a set of tubes (moulded into the facepiece or not), a deflector pouch, or deflector plate to prevent the lenses from fogging.

Dr. Jules Tissot was the inventor of a breathing apparatus designed for mine rescue and used since 1907, before WW1. These devices were recovered at the end of April 1915 to be sent to the French army. Although they were used seldom, the only 250 copies existing were all used. On April 22nd 1915, after the appearance of poison gas, Dr. Tissot initiated a research on making a new apparatus for protection against gases. This research led to a device consisting of a mask made of sheet rubber that was glued together (even the head harness). Glass eyepieces were attached to the mask with a crimped metal ring, and an air inlet/outlet system consisting of black varnished copper tubes that housed the air tube and the valve similar to that of the previous 1907 apparatus.

Filtration was carried out by a rectangular, backpack-sized metal box containing two layers of filtering materials: two layers of iron straw containing iron potash and a second layer consisting of wood chips soaked mixture of castor oil and sodium bicarbonate. The canister was carried on the back, due to its large size, and on top of it, there was an opening allowing the hose connecting the filter box to the mask portion to be connected to the filter via threads, and on the bottom there was an air intake port with a rubber disk inside to permit air inhale, but not exhale. When not in use, the port was closed by a rubber plug.

The prototype was sent to the Commission and the various members, which conducted the Lebeau laboratory test on January 8, 1916. The test subject entered the test chamber filled with benzyl bromide and phosgene, and was observed as gas was gradually added to the atmosphere. After 20 minutes, feeling a slight tingling in the eyes, the experimenter came out of the room and the test was concluded. The level and quality of vision was improved by the Tissot tubes due to less fogging. Dr. Tissot had sought to avoid fogging on the panes of glass by cooling the inside of the eye by an ingenious system: each time the user inhaled, air arrived in the mask by two pipes around the eyepieces, so they were constantly exposed to fresh cold air, preventing condensation. The two tubes were made of rubber and connected from the bottom of the lenses to the pipe leading to the hose.

Exhale breathing was easy as well, as the "flapper" type exhale valve was located directly on the mask on a pipe angled upwards to reduce the exhale resistance. The intake tubes were soldered to this. Inside the mask and in its lower part, there was a folded wire spacer connected to the outlet port in the mask that prevented collapse of the mask upon inhaling. A second test was conducted on January 14th, outdoors in Satory where Dr. Tissot was invited. The purpose of this test was to have the test subject move through a wave of phosgene, chlorine and smoke gas, 50 metres from the gas canisters.

Lebeau, wishing to make the comparison with the older TN mask, along with Tissot's device, timed how long one could go without feeling the slightest problem. Upon proceeding with these two tests, the Tissot apparatus was ruled as a good respirator. The Commission therefore proposed to continue development of the Tissot Apparatus, not to substitute for the other masks in service, but to replace oxylithe devices or the Draeger Rebreather. These two types of gear are used in high-concentration toxic environments, since they operate in a vacuum using supplied air. Their main disadvantage is their period of use, which may not exceed half an hour. The Tissot Apparatus was therefore a real advantage, but these expectations needed further proof and additionally, to establish duration of use with different types of gases and concentrations.

After extensive tests, Lebeau found out in light gas concentrations, the device could work up to 50 hours before being exhausted, and 30 hours in extreme conditions. It protected against all period chemical warfare gases, unlike some of the older masks. The mask was considered one of the best of that time, and the Committee decided to produce an initial 1,000 units to continue research in order to arrive at a production model. On April 29, 1916, testing was concluded. On this date, 450 Tissot masks had been manufactured and 50 were tested by a company that produced toxic gases. Unanimously, the Tissot apparatus was chosen and adopted. Delivery of the masks to the frontline started that same year on the month of July.

The mask comes in a large rectangular wooden box painted blue with large black markings that read: "APPAREIL T" (Apparatus Tissot) was what the apparatus was contained in, because it was not intended to be worn by a regular infantryman or soldier who needs to move from place to place constantly. It was considered a special sector apparatus that remained in place in a fixed position like its user (e.g. machine gunners, artillerymen, snipers, communications troops and combat engineers).

Overall, 30,000 units were produced. Later, Lebeau added an additional cartridge of sawdust that connects under the filter drum, at the air intake port. This cartridge is threaded on the upper side and has straps with a tenon and bayonet latch closure (like on a mason jar) to hold it against the filter on its underside. It allowed protection against smoke. However, it was necessary, for it needed to be soaked for 5 minutes in water before use to moisten the chemicals impregnated in the sawdust and activate them. In the month of August, 1916, he proposed to change the layer of wood chips soaked in castor oil to a layer of charcoal. This research was conducted in parallel with a new mask, the A.R.S, with filter cartridge also containing charcoal. The nature of wood use and preparation of coal had to be fixed carefully. Lebeau researched on this subject by the end of 1916 and the Tissot apparatus' new change of charcoal was adopted on March 10, 1917. Earlier models will bear a distinctive mark - a black 5-pointed star painted on the upper surface of the box and the later boxes, a yellow star. The new layer will contain humid air to ensure protection against opacity (smoke).

These new devices began to appear in the battlefield at the end of June, 1917. The coal would quickly dry up and Lebeau needed to replace this mode of the smoke filter with a cylindrical additional cartridge filter with the soaked charcoal, screwed under the drum. These cartridges were threaded on each of their bases and were painted yellow to distinguish them from the dried up canisters. They also provided better protection against Acrolein. The newer cartridges appeared in August, 1917.

At the end of 1916, a cylindrical valve protector for the fragile, "flapper" type outlet valve was added to avoid being damaged. Always with Lebeau, a new development was made in late 1917. The mask's glued sheet rubber facepiece tends to tear after a period of time, so some copies would thus be manufactured in the same way as the new A.R.S. mask: the rubber will be replaced with a rubberized fabric impregnated with boiled linseed oil that was twice as thick as the original.

These new masks were available in three different sizes. A new cartridge was later developed, containing coal, but with an added hydrophilic cotton to stop arsines. It was distributed at the beginning of 1918 and included a distinctive red paint mark. In January 1918, Lebeau replaced the soda that wetted the iron straw containing iron potash with soda lime, to avoid a repeat of an accident that occurred -- when the soda in the filter left containment and entered the mask, the wearer, upon inhalation, received severe chemical burns. The change was made in summer 1918. After this incident, to warn others of the dangers of the old filters, the filter boxes of the former models charged with soda, were marked with the inscription: "Don't forget to purge the container after each use to prevent the flow of clothes-burning liquid".

More than 100,000 units of Tissot large model were manufactured until the Armistice was declared in 1918. E.C.M.C.G. provided the manufacture of specific Tissot apparatuses for the protection of personnel against chemical weapons. A Tissot filter was also developed for vapors called P.V.N. followed by a model intended for blowing snow. Then came the 1917 Tissot apparatus, small model.

The Tissot mask has proven itself to be more effective than other masks in service in the French military, but its size prevented men to move with ease. The idea of making a Tissot apparatus lighter and smaller that it could be carried unimpeded very rapidly, was essential, as chemical warfare kept advancing. On the German side, parallel to the use of supalite, commissioned 150mm "T" shells of a mixture of tear gas substances, whose effects appeared to be more important than those of the components taken separately. Similarly, the use of dibromo ketone derivatives were used instead of less efficient monobromo derivatives. The French, on the other hand, at the end of 1916, introduced powerful and toxic chlorosulfate of ethyl or sylvinite on the battlefield. Dr. Tissot was therefore requested by the Commission to make a smaller model facilitating a more general use of the apparatus.

By late November 1916, he proposed his prototype, with little difference from its big brother, if not by the size of the filter cartridge, and a few minor details. Lebeau hosted different trials, not only on the nature of the different gas against which the apparatus protected, but on the reliability and durability of the device also. It will be violently dropped many times, then hammered and abused. Upon failing the durability test, the mask was still remarkably accepted upon passing the function test, and on December 2, 1916, the Commission will adopt the new model; the development of filling the canister will be provided by Lebeau, and will result in serving alongside with the large model Tissot and the new A.R.S. mask in service.

The filter drum (canister) contains activated charcoal, and once again, iron straw impregnated with potash. The first units arrived at the E.C.M.C.G. on March 27, 1917. The filtration was comprised of seven layers of gauze impregnated with soda, and a load of activated charcoal retained between two metal grids. The protection offered by the mask and filter was excellent against most agents of the time until the introduction of German arsines in summer 1917. Diphenylarsine chloride could penetrate the compresses and coal.

Lebeau determined that only the cotton wool could stop these substances, so he added an additional cartridge loaded with cotton and fixed two straps to the same filter, and the improved model was produced and distributed early 1918. The shape of the body of the filter box changed slightly to introduce the additional cartridge. In the summer of 1918, the soda impregnating the straw of iron was replaced with soda lime, in the same way as the grand model Tissot. The new filter canisters were distinguished from the former by the lack of drain holes at their base, and did not have a red band of paint. Until the end of the war, the small model Tissot will play an increasing role in the chemical protection of troops.

U.S. Signal Corpsmen Wearing Small Model Tissot Gas Masks

The U.S. Army field-testing the French Tissot Apparatus (Small Model) by demonstrating its ability to utilize the use of speech, for the mask had no uncomfortable noseclip and mouthpiece. These tests helped the U.S. pave the way towards making the Akron-Tissot & Kops-Tissot Gas Masks throughout 1918.

In October, 1918, it was decided to permanently replace the model grand Tissot production by the small model. By this date, all manufacturing had stopped due to the end of the war. By the time of the Armistice, 590,000 copies of the mask had been made. The U.S. Army would later field test the small model Tissot apparatus for its capabilities and further develop the design and incorporate its features into their own masks. Examples of later models such as the "Kops-Tissot" of summer, 1918, and the "Akron-Tissot" of June, 1918 are a testament to the mask's continued evolution.

Almost no examples of this mask survive. After almost 100 years since it was last manufactured, most Tissot masks have been lost to old age and due to the period materials not being as resilient to ageing as today's synthetic rubbers. Aside from a few remaining filter canisters, a Small Model filter, hose and valve system without a facepiece is known to be in the possession of a collector named Boris Plotnikoff. The one complete surviving example that is known to exist is owned by an unknown collector.

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