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Rinsing Film.-If possible, film and paper should be rinsed between developing bath and fixing bath. In the case of aerial film, it was customary to dip the reel in a tank of clean water, moving it up and down for half a minute, then to transfer it to a second tank of clean water, to be moved up and down for half a minute, and then to the fixing bath. For paper and for small negatives, it was customary to have the rinse water acidulated with 3 ozs, acetic acid of 28 per cent. strength, or 1 oz. of the 99 per cent. glacial acetic per gallon of water. This stops development instantly, and ensures to a large extent that all developer has its alkaline content thoroughly neutralized before the print or film enters the fixing bath. A fixing bath which becomes alkaline is very bad, especially where the solution is warm; dichroic fog and stain may result-impossible to remove afterwards. In tropical development it is important that the fixing bath be always acid in reaction, that it have more than the customary amount of acid hardener, and that it be renewed frequently. The acid short stop for rinsing is an insurance that the acid hardener of the fixing bath does not get neutralized.

Fixing Bath. For the large tanks we used 40 lbs. of hypo to 20 gallons of water. A freshly made-up hypo bath is considerably lower in temperature, due to the passing of the crystals into solution. While a slightly cool hypo bath is desirable, it should be remembered that the emulsion on film or paper, when taken from a very cold hypo solution to warm wash water, is apt to break loose from its supporting base. Solutions should not differ more than a few degrees in temperature.

Hardener.-One pint, or 16 fluid ozs., of the following hardener, is added to each gallon of the hypo fixing bath :

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The above solution is slightly yellow when first mixed, but becomes quite colourless; if it is milky in appearance, it is evidence that the chemicals have been mixed in the wrong order. When added to the hypo solution, the combined solution should still be colourless. If there is much vegetable matter in the river water used, as is apt to be the case in the tropics, the alum will coagulate the slime, carrying down suspended particles; there is then apt to be half an inch of moss-like flocculent stuff at the bottom of the large fixing tank. This does no particular harm if not stirred up; it is better to remove it by bailing off the top liquid into an enamelled bucket. Pour back the top liquid, add the top of the solution in the bucket after allowing it to settle, and throw away the residue.

If film shows any sign of reticulation, it is evident that not enough hardener has been added, and more should be put in the fixing bath than that indicated. The fixing bath should not be used when it becomes frothy; a new bath should be made up. Watch the fixing bath; almost all hot-weather troubles come from an incorrect fixing bath.

Apparently the secret of developing film at the river temperatures that prevail in the Amazon Basin, 80° to 85°, is to develop reasonably quickly (not over four minutes) so that the gelatine will not have too much time to swell, and to fix in an acid bath that has enough hardening agent to shrink the gelatine of the emulsion to a hard surface.

Purification of Water.-River water in the Amazon Basin is quite free from inorganic salts, such as lime; for washing it is what is commonly termed "soft" water, producing a lather freely with soap. It contains considerable vegetable matter, some yellow mud, and some sand in suspension. If given one or two hours to settle, much of the mud and sand will be found at the bottom of the container, and some of the vegetable matter is carried down at the same time. The handiest scheme for getting fairly clean water, therefore, was to bring it from the river in ordinary 5-gallon gasoline or kerosene tins, the tops of which had been partially cut out to faciliate filling and emptying; these cans were allowed to settle for at least two hours and preferably five, being filled just before sunset. When to be used, some 41⁄2 gallons was carefully poured off into tanks or trays and the remaining half-gallon thrown away. A secondary advantage of this method was that the cans quickly acquired night air temperature, and surface evaporation still further reduced the temperature. It was often possible to get water as cold as 79°, and very occasionally, if a night breeze was blowing, water as cold as 75°. The river water never ran over 85° where there was even a moderate current, and development at 82° to 85° offered no difficulties; if the water could be brought to 79° or 75°, so much the better.

Delay before Developing. It is important that all negatives be developed in the tropics as soon as possible after exposure. However this is often impossible, and steps are necessary to preserve the emulsion from moisture. In the case of aerial film, the best practice is to seal all the joints of the cover of the camera magazine to prevent circulation of air. One sealed exposed aerial magazine was unavoidably left at Vista Alegra (less than 2° off the equator) during fifty days of almost continuous rainfall, yet on development it showed no signs of deterioration. This magazine was sealed with Johnson & Johnson "ZO" adhesive tape, 1 inch wide; this is very good tape and holds up well in the tropics; when it is pulled off, the paint usually comes with it.

For Graflex and Kodak cameras it seems best to use roll film exclusively, to use the six exposure rolls, to finish exposing the roll the same day, and to reseal it with tape in the same tin container from which it was originally taken, before nightfall. As these hand cameras differ from aerial cameras in having leather bellows, a change of air takes place at each using; consequently it does no good to attempt to seal the back of the camera. The small rolls will absorb little moisture where a series of exposures are made within a few hours, and the film, when put back in its can, is in practically the same state of dryness as when packed at the factory. Thus resealed, it may be developed months afterward. It should be protected very carefully from direct heat rays until developed. For the smaller negatives, a special box, about the size of a kerosene case, was carried. This had a zinc case inside, with separate cover. The inside of the wooden box was lined with sheets of asbestos; the outside was covered with canvas, so arranged with flaps as to shed water. This box was rainproof, and to a very large extent sunproof.

Aerial film, not being required so often, was kept in its original sealed tins, inside its original cardboard box, and was wrapped in a blanket or other clothing, and kept well to the centre of duffle bags, kerosene cases, or other containers-the object always being to keep it from getting hot from the sun's direct rays during the daytime. Motion-picture film, received from New York in the hold of ocean-going steamships, was repacked at Manaos for up-river shipment; the sealed cylindrical tins, inside their cardboard boxes, were packed in rectangular tin cases, which were soldered tight. These tin cases were supported inside wooden cases in such a way that there was a clear air space of more than 1 inch all around; a few ventilating holes were cut in the outside box. Thus packed, there was little danger of the film getting hot, even if exposed for hours to sunlight on the open deck of a river steamer. River steamers distribute their freight all over the decks, particularly if it be comparatively light and bulky, and a shipment of film is very apt to be where the morning or afternoon sun, or even the mid-day sun, can strike it. Reshipped in launches, film stands a somewhat better chance; transferred to canoes, it is often covered with canvas or with native thatched toldas, or with grass mats. However, it may be the top unprotected box at any time, and the only safe way is to insulate it so far as possible against heat.

Where much work is to be done, it certainly will pay to take chemicals and trays as far as possible for the purpose of developing plates and small film, even if the trays and chemicals have to be abandoned when transportation becomes too difficult. In the meantime part of the film will have been developed, and will not then require special attention if in watertight cans, and a line will have been secured on correct exposure times for subjects, dark-skinned or light-skinned, in the open or in the woods. Motion-picture film, of course, cannot be developed in lengths, but small pieces cut off and developed serve to ensure that the instrument is working properly, and that the right shutter opening and diaphragm stop are being used.

Developing and Drying.-A canvas tarpaulin is thrown over the roots of a tree, or over a ridge pole erected for the purpose; two empty kerosene or gasoline cases, always available, are used for a table, and the fun begins! The negatives are put through several changes of water,

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and then left until morning, being sure that they are completely immersed. If the fixing bath contains sufficient hardener and this is the important feature-the negatives will not soften. It is useless to attempt to dry them at night-they will not dry. Moreover, in the dark the wet emulsion offers a tempting meal to ants, roaches, and other insects, and it may be found at daylight that patches of several square inches are perfectly bare of emulsion. After sunrise the negatives dry fairly fast, if suspended on clips on stout twine, where the morning breeze -there usually is some motion to the air-can strike them. This means, of course, that it is not advisable to do any developing if an early morning start in canoes is scheduled, but to wait until the party camps over a day. There will be no trouble from reticulation, from frilling, or from the emulsion running-if the fixing bath only contains enough ordinary hardener !

Exposure Time. The fraction of a second necessary for full exposure is about the same as in the United States, notwithstanding the fact that the sun is more nearly overhead on the Rio Branco. It seems that the atmosphere, holding a large amount of water, filters out a certain proportion of the actinic light. Because of this filter action, the human body is protected from the shorter waves from the sun, and sunstroke is unknown in Central Brazil. Panchromatic film, highly sensitive to other colours besides blue, holds its speed wonderfully well throughout the day, and it is possible to get full exposures much earlier and much later than with ordinary film.

Care of Cameras. If cameras are given the same attention that is ordinarily given to clothes, that will be quite enough. When clothing, during a rainy spell, is known to be getting damp, it is spread out for drying and airing on the first sunny day; half an hour or an hour on a black rock or ledge, under a fierce sun, will check any mould and dry it thoroughly. At the same time any instruments with leather and wooden parts, such as Kodaks and Graflex cameras, should be dried out. The backs should be removed, and the lens if possible, to let air circulate through; the leather parts should be wiped free of mould. Sometimes trouble is experienced with the reflex type camera with the mirror sticking from general swelling of the wooden box; thorough drying in the sun will usually make it operate all right again. A very little light oil on some of the working parts is advisable. Equal attention should be given the carrying cases to see that they are thoroughly dried out inside.

Aerial cameras, made almost entirely of metal, require practically no attention, especially if the magazines are sealed with tape.

On coming quickly down from the higher altitudes, it is often useless to attempt photography with aerial cameras, as the cold lens will condense water on its surface as soon as the warm moisture-laden lower layers of the atmosphere are reached. Going up, of course this difficulty does not exist.

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Stevens with Fairchild Aerial Camera and Maionggon Indians at Kujuma

Silvino Santes at Boa Esperança

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