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in the British army at the front was supplied with this form of respirator. Although rudimentary, it gave useful protection.

Meanwhile chemists and physicists were at work on both the French and British fronts investigating the facts and advising on temporary protection. The day after the first gas attack, in- structions were issued to keep buckets of solution of bicarbonate of soda in the trenches; the men were to dip their handkerchiefs in the solution and tie them round their mouths in case of gas attack. More efficient respirators were considered, also the use of large fans for clearing the trenches of gas, and direct fighting of the cloud by spraying neutralizing agents into it. Thousands of Vermorel sprayers were sent out, for clearing trenches and dug- outs. The dispersal of clouds by shelling and by explosions was tried, also lighting fires in front of the trenches to heat the cloud and cause it to rise. None of these methods were really effective in stopping clouds, and attention was gradually concentrated on direct defence by masks.

The first improvement on the respirator, which was introduced in the War Office a few days after the attack, was known as the Smoke helmet or Hypo helmet, a kind of Balaklava helmet made of flannel or thin serge, covering the head loosely and reaching below the neck, round which it was tied. The eye- pieces were made of mica. This helmet was impregnated with hyposulphite, soda and glycerine solution, and carried in a waterproof bag. It gave satisfactory results for some time. Pending the complete supply, the increasing use of lachrymating shells by the Germans gave rise in June to a demand for goggles.

During 1915 the helmet was improved by the introduction first of phenates to protect against phosgene (when it is called the P helmet) and later by the further addition of Hyomine (when it was called the P.H. helmet), to ensure protection against phosgene and prussic acid. A respiratory valve and mouth-tube was also inserted in the P. and P.H. helmets, and this added to their comfort and efficiency.

As the use of other gases was foreseen, such as phosgene and hydrocyanic acid, a more effective protection than could be put into cloth became necessary. Thus the " box respirator " type was developed, and gradually issued during 1916. The general type of these consisted of a mask or face-piece into which entered a flexible tube issuing from a metal container which held chemicals, through which the air was breathed. In the earlier patterns the air passed through the tube into the space between the mask and the face; but as it is very difficult to get the mask to make an airtight fit round the face, the tube was extended and ended in a mouth-piece which fitted closely to the lips, while the nostrils were closed by a nose-clip. The container and mask were carried in a knapsack. The mica eye-pieces were replaced by celluloid, and eventually by triplex glass, which does not splinter when broken and remains airtight.

The introduction of a container for the neutralizing and absorbing agents gave free scope to chemists to provide against all kinds of poison gas. In this connexion it is worth recording that the British gas-mask did in fact give efficient protection from its introduction to the end of the war.

The containers were filled with alternate layers of charcoal and composition granules. The charcoal absorbed gases, and the granules, whose composition could be varied indefinitely, absorbed and neutralized them. The container had the further advantage that its contents could easily be renewed.

This type of respirator continued in use until the end of the war but was subject to continual improvement. No effort in this direction could be spared seeing that any defect in the manufacture or adjustment of the mask might mean death to the wearer. Constant progress was made with the British and French patterns, and the Americans when they entered the war took up the question very thoroughly. They, like the French, had the advantage that their chemical service was a separate branch of the army with the offensive and defensive sections working under the same head. Among other defects the air-tight fitting of the mask to the face needed a great deal of study and experiment. The eye-pieces gave trouble because moisture would condense on them both outside and in. This was partly cured by

using a soapy solution on the glass. The whole apparatus had to be made as little cumbrous as possible, and so adjusted with its knapsack that it could be very quickly taken out and put on. The use of the mouth-piece and nose-clip was very trying when worn for long periods.

In 1918, the Tisset mask was introduced in France, which did away with the mouth-piece and met the difficulty of condensation by causing the cold air from the inlet-tube to pass across the eye-piece in entering the mask. This type, which was adopted and improved by the Americans, was known as a " single-protection " respirator. Its weak point is that if the face-piece is torn, or does not fit properly, protection is lost.

The provision of the charcoal for the containers opened up a wide field of investigation. For absorbent purposes a very dense charcoal was required. Experiments made in the United States showed that coconut-shells gave the best form of charcoal for the purpose, but their preparations were on such an extensive scale that they calculated that they would require a supply of 400,000 tons per day of coconut-shell, which were obviously not obtain- able. After coconut-shells the best carbon was obtained from fruit- stones such as peach, cherry, etc., and Brazil and other nut- shells. Carbon obtained from hard wood, such, as the ironwood was of less efficiency.

The scale on which the United States worked is shown by the following figures given by Farrow of the production of protective materials up to the date of the Armistice, the great bulk of which were produced in the last four months of the war:

Production up

Material. to Nov. n 1918.

Respirators. . . 5.276,515

Extra canisters

Horse masks

Bleaching powder (tons)

Extra antidimming (tubes)

Sag paste (tons)

Dugout blanket oil (gallons)

Protective suits

Protective gloves

Dugout blankets

Warning devices

Trench fans

3,144,485 366,529 3,677 2,855,776

95,000 500 1,773 159,127

33,202

29,977

The sag paste mentioned in this list was an ointment used for the skin to protect it against mustard gas, the protective suits and gloves being for the same purpose. The blankets, which were to seal the doors of dugouts, were made of specially woven cotton treated with a specially heavy oil. The warning devices were mainly watchmen's rattles and Klaxon horns.

From the beginning gas schools were established on all army fronts, where men were taught the use of the masks and made to enter gas chambers with masks on to get proof of the protection afforded. Similar schools were established by all the nations at their gas defence headquarters, where experiments could be tried. The result of such work is well shown by the following extract from Farrow's description of the American gas service:

" There was a special field-testing section of the Gas Defence Division composed of about 150 men who were trained to the min- ute in field manoeuvres and did most of their work in gas-masks. They were constantly in and out of gas with regular production and experimental masks. They played baseball in them, they dug trenches, laid out wire, cut wires, and fought sham battles at night, both with and without actual gas. The work of this section even went so far in the case of the later design as to include a test where six men worked, played and slept in the masks for an entire week, only taking them on for 30 minutes at each meal-time, and each day entering high concentrations of the most deadly gases without any ill effects whatsoever to the wearers. When it is remembered that eight hours was the limit of time which a strong man could wear the old-type mask, something of the efficiency of the new mask may be realized."

These of course are experimental results with selected men, which generally differ widely from those obtainable in the field. They only show the great improvement made in patterns of respirators before the end of the war. The fact remains that any efficient respirator is a source of fatigue as well as a great incon- venience. British experiments have shown that in hill-climbing with and without respirators, there is a marked difference in the increase of heart rates and rates of breathing under the former