melts at exactly 100° C., fastened at A, keeps the electrodes at B and C apart. The entire thermometer D is then placed in the box E for protection, and this is placed in the chamber or in the inside of bunIdles to be disinfected. The insulated wires from F and G are connected with a battery and bell. As soon as the temperature reaches 100° C. the little metal stick melts, the contact is made between B and C, and the bell rings. This form of thermometer is more accurate than the pyrometers, which depend upon the contact being made by the unequal expansion of a compound metal bar, for the reason that moisture collects upon the electrodes and an electric contact is sometimes made before the metal parts actually touch, thereby giving false readings.

PAUL ALTMANN
E

A

FIG. 150.-AUTOMATIC THERMOM

ETER.

Steam chambers must always be provided with galvanized or copper hoods to prevent rust-stained drip from soiling the clothing and other objects exposed to the steam; gages to indicate both vacuum and steam pressure, and a safety valve to prevent over-pressure in the chamber. The amount of pressure from the boiler is regulated by a reducing valve in the main steam pipe.

For convenience in handling the goods cars are provided, of light wrought-iron construction, with movable trays made of galvanized screens; also bronze hooks at the top of the car, permitting the articles to be laid upon the trays or to be hung up on the hooks.

In the accompanying diagram (Fig. 151) the method of installing the steam chambers in the disinfecting shed of a quarantine station is shown. It will be noted that the cylinders open on both ends, and that a dividing wall running across the building separates the receiving end, where the infected objects arrive and are prepared for disinfection, from the discharging end, where the contents of the chamber are aired, dried, and repacked after disinfection.

This separation is essential where a large amount of disinfection is done for a variety of diseases, as, for example, in a municipal disinfecting establishment or at the quarantine station of a busy port. It is true that the infection of certain diseases is not apt to contaminate the surroundings, and in such cases there would be little risk in taking the disinfected articles out of the same end of the chamber from which they are put in, especially if the exposed surfaces are mopped with a disinfectant in the interim. But this is a risk that need not be taken; in fact, all well-regulated disinfecting plants maintain a rigid separation between the two sides, never allowing both doors of the chamber to be open at the same time, and providing two sets

of workmen, one for the "infected" and one for the "disinfected" side.

10

The chambers must be loaded with care in order to obtain reliable

Storage
Disinfected Clothing

T

FIG. 151.-PLAN SHOWING THE METHOD OF INSTALLING THE DOUBLE-ENDED STEAM CHAMBERS AT A NATIONAL QUARAN

TINE

STATION.

results and to avoid injuring the articles exposed to the process. The packages must not be too large or crowded too closely, for, although the vacuum facilitates the penetration of the steam, there is a limit in this regard; it takes so much longer for disinfecting agents to penetrate dense packages and bundles that there is little saving of time and a distinct loss in trustworthiness. Steam cannot penetrate compressed bundles of rags, bales of cotton, feathers, hair, or other packages of merchandise which are often presented for disinfection. Fortunately, it is seldom necessary to disinfect such packages. When, however, this is called for it is essential to open and properly expose such objects to the action of the disinfecting agent.

In the municipal disinfecting stations of Paris the process of applying steam under pressure is as follows: The pressure is brought up to 15 pounds in the chamber and held there five minutes; then released. The pressure is again brought up to 15 pounds, held there five minutes, and again released. This is repeated three times, when the disinfection is completed. The cylinders are fitted with an in

genious arrangement for the automatic registration of the process. Each chamber is connected by a small copper tube to a register with a moving pen and revolving drum carrying a chart. The horizontal lines 1 to 10 on the chart each represent a pressure of one-tenth of an atmos

phere, and the vertical lines represent five minutes in the revolution of the drum. Each steaming is represented thus:

These charts, which can be removed only by the chief of the station, are sent each day to the Inspector-General, and give a perfect guarantee that each steaming has been done as directed.

CHAPTER III

CHEMICAL AGENTS OF DISINFECTION

GASEOUS DISINFECTANTS

A gas is an ideal weapon for destroying such invisible foes as we have to deal with in public health work, especially for terminal disinfection. By reaching all portions of a room or confined space a gas lessens the risk of overlooking any surface upon which the infective agent may be lodged, but the ideal gas for this purpose is still to be discovered.

There is practically only one gas suitable for general application, viz., formaldehyd. This substance comes nearer being an ideal disinfectant than any of the gases in general use. It is not poisonous, does not injure fabrics, colors, metals, or objects of art and value. Formaldehyd, however, has distinct limitations, which are dealt with more in detail under the description of the gas.

Sulphur dioxid is too destructive for fabrics, colors, and metals for general use. It is a better insecticide than germicide. It is very poisonous to all forms of animal life, which makes it valuable in disinfection against insect and animal-borne diseases. It has no equal for the fumigation of the holds of ships, cellars, sewers, stables, and other rough structures infested with vermin.

The very poisonous and destructive nature of chlorin gas contracts its usefulness to narrow limits.

Hydrocyanic acid gas is too poisonous to use in the household, and is limited in practice to the destruction of infection and vermin on board ships, in warehouses, greenhouses, granaries, railroad cars, and other uninhabited or isolated structures.

None of the gaseous agents can be depended upon for more than a surface disinfection. They all lack the power of penetration.

Preparation of the Room. -The preparation of a room or space to be disinfected with a gas is a matter of some importance. A larger amount of gas than is thought possible is lost through leaks by diffusion and absorption and in other ways; therefore the room should be made tight, all cracks and crevices should be well closed by pasting paper over them or by caulking with suitable material of some kind. Do not

forget to close the registers, flues, hearths, and ventilators, and look carefully for openings in out-of-the-way places. Then expose the objects in the room so that the gas may have ready access to all the surfaces. Hang clothing, bedding, and fabrics upon lines strung across the room; move bureaus, beds, and furniture away from the walls, open doors of closets, drawers of bureaus, lids of boxes, and the like so that the gas may freely enter and diffuse to all corners.

While the articles in the room must be arranged so that the gas may freely gain access to all surfaces possible, the mistake must not be made of going to the opposite extreme of disarranging the contents. of the room too much, for the same surfaces should be exposed to the gas that were exposed to the infection.

The strength of the gas and time of the exposure necessary to insure disinfection have been determined by exact laboratory experiments, but the conditions found in actual practice are so variable that we must allow for a liberal excess to make up for inevitable wastage. Wind pressure also seriously influences the efficiency of gaseous disinfectants in a confined space. Much more air than is commonly thought possible forces its way through cracks and through the walls themselves. The wind pressure may thus drive the fumigating gas entirely away from one side of the room. It is only necessary to stand upon the leeward side of a structure being disinfected with sulphur dioxid or formaldehyd to realize the great quantity of gas blown from the enclosure.

Formaldehyd Gas.-Formaldehyd is the most generally useful and one of the best disinfecting gases that we possess. Its superiority depends upon its high value as a germicide, its non-poisonous nature, and upon the fact that it is not destructive. The secret of successful disinfection with this substance is to obtain a large volume of the gas in a short time.

Formaldehyd (HCHO) exists in at least three well-recognized isomeric states:

(1) Formaldehyd (formic aldehyd) is a gas at ordinary temperatures, colorless, and possessing slight odor, but having an extremely irritating effect upon the mucous membranes. At a temperature of about 20° C. the gas polymerizes into paraformaldehyd, known commercially as paraform.

(2) Paraform is a white substance, unctuous to the touch, soluble in both water and alcohol. It consists chemically of two molecules. of formaldehyd. It is this substance which is supposed to compose the commercial solutions of formaldehyd known as formalin, formol, etc.

(3) Trioxymethylene is formed by the union of three molecules of

1 Formaldehyd is the gas, formalin is the aqueous solution of the gas.