EXPEDITION TO THE RIVER NIGER
DURING THE YEARS 1841-2.
The system of ventilation adopted in the vessels of the Niger expedition, according to the plans proposed by Dr. Reid, presented the first systematic attempt that had been made to place every compartment of a ship under the immediate and direct control of a ventilating power: it may be proper for me therefore to give a separate notice on this subject, particularly as so much attention is now directed to this department, as a means of improving health in the navy.
The leading principle which has been advocated by Dr. Reid, in respect to the ventilation of ships, is, that a system of tubes should be formed in every ship, and so connected together, and placed under the operation of a power that can always be depended upon, that under any circumstances, fresh air can be infused into, or vitiated air extracted from any compartment of the vessel, whether in the hold, or on any of the decks, the amount of power placed upon the ventilating apparatus being proportional to the service in which each ship may be engaged, and the number of people crowded in a given space. Dr. Reid’s estimate of the amount of air required for ventilation, being far above that which had been previously adopted, his arrangements necessarily were on an extensive scale, and formed a marked feature in each of the steam-ships.
Special arrangements were also introduced with the view of endeavouring to combat some of the evils that were known to prevail in the atmosphere of African rivers; but in respect to these Dr. Reid remarked, from the commencement, that they would only be viewed in the light of an experiment, or as he stated in the "Friend of Africa," "It must be obvious, that it will be impossible to estimate precisely the extent to which such an apparatus may prove beneficial until some specific information as to the peculiar chemical qualities of the atmosphere of the Niger shall have been obtained."
In ordinary circumstances when windsails, fanners, or other powers have been introduced with the view of promoting ventilation, they have in general acted locally, with various effect, influencing powerfully the state of the atmosphere at one place, while in others it remained comparatively unaffected. But the great object of the system of tubes introduced, was to produce a precise effect, wherever the power of the ventilation was most essential, the valves regulating, according as they were set, the amount of power brought to bear at a given time, upon any individual compartment.
In the accompanying woodcuts, an illustration is given of the system adopted, excluding the minutiae of the arrangement of the individual tubes, as were they shown in the form in which they had to be made, from the progress in the building of the ships before the introduction of ventilation was decided upon, they would not communicate so distinct a view of the system.
In addition to the ventilation that could be commanded by the apparatus now referred to, every compartment of each of the ships had two communications with the external atmosphere, capable of being opened or shut as might be required, and of affording accordingly independent ventilation. One of these communications conveyed fresh air to the lower part of the cabins, and the other, being placed above, allowed the warm and vitiated air to escape. A connexion was also established between the paddle-box and the general system of ventilating tubes, so that on extreme occasions the power of the paddle could be brought into operation in calm weather, with the view of removing vitiated air. It was also intended to have made the chimney available for this purpose, but the progress made in building the ships before the ventilation was begun precluded this arrangement from being carried into effect. Fig. 1 gives a profile illustrating more particularly VENTILATION ON THE VACUUM PRINCIPLE. This mode of working the apparatus was generally adopted in the Albert, until the vessel arrived in the Niger. The letter F represents the fanner or ventilating machine, receiving the vitiated air from the various compartments of the ship, and discharging it at S.
A fanner operates essentially by disturbing the equilibrium of the pressure of the atmosphere. As the blades revolve, the air in immediate contact with them is conveyed towards their extremities by the centrifugal force, and propelled at any opening in the circumference S. In this manner a comparative void is left within the casing of the fanner, and the tubes connected with the different compartments communicating freely between them and the interior of the apparatus, the pressure of the external atmosphere forces air from them to restore the equilibrium, and this process goes on incessantly so long as the motion of the fanner is sustained.
The fanner was put in motion by the machinery connected with the steam-engine. It was also occasionally worked by the Kroomen, and in general during the night, when in the river, by the stream, as when the engine was disconnected with the paddles they were moved by the current, the paddles in this case acting as water-wheels, and the force thus obtained was applied to the movement of the fanner.
Letters E E indicate the principal distribution tubes which extended fore and aft throughout the ships. They may be compared to the great arteries or veins of the body, establishing a connexion and circulation throughout the whole system, HHHH point out the lower deck, and the manner in which air passed from it to the distribution tubes. When the valves abaft were shut, the ventilating apparatus worked with much more power forwards; and in the same manner, when the forward valves were closed, its influence was correspondingly felt in the principal cabins. It was always a great point to adjust the valves in such a manner that the power of the ventilation should work proportionally throughout the whole ship, according to the wants in each individual compartment.
In every compartment of the ship, communications could be established between the distribution tubes and the hold, so as to remove directly any vitiated air there, and prevent its affecting those who occupied the decks above. Thus, in the midshipmen’s berth, division G, this arrangement is represented in operation. The same could be done in the lower deck, HHHH, by altering the adjustment of the valves; and in short, in the midshipmen’s berth, and in the other compartments of the vessel, the air could be made to move in either direction as might be considered desirable, P and K represent some of the varied arrangements for diffusion adopted below or above in the individual cabins.
In L a peculiar arrangement is shown, such as could be put in operation when the hold produced no offensive atmosphere. By this mode, when the external atmosphere was very warm and the water cold, the air could be conveyed in the first place to the hold, and cooled there to a certain extent, by impinging on the iron bottom in contact with the water before passing to the compartment which it was intended to supply, T R and V illustrate the action of the gunwale-tubes on the after-cabin D, the influence of the other ventilating arrangements there being suspended by closing the valves. Such was the system adopted for the extraction of air by exhaustion: and extensive as the arrangements may appear, still when the steam-vessels arrived at the Niger, more rather than less ventilation was desirable. Dr. Reid has remarked, "Few individuals, excepting those who have visited warm climates, are ready to credit the great supply of air that is indispensable for health and comfort in such countries, the all-subduing influence to many constitutions of sudden or extreme changes in respect to the quality of the air that surrounds the person, and the extent to which the mental faculties as well as the bodily strength are often prostrated by such causes. Proceeding on the assumption that no supply of air that was likely to be provided by artificial means would exceed the wants of the system in the Niger expedition, the demand made in respect to the power of the apparatus was limited solely by the opportunities afforded for giving effect to the arrangements proposed; and when their extent became the subject of special remark, my reply on board these ships while they were still at Liverpool, was "that even if the whole ship were appropriated for ventilation alone, it would not be possible to guarantee a certain result, as the quality of the atmosphere of the Niger had never been made the subject of experimental examination, and still less the precise nature of the evil which proved so fatal in former expeditions."
The second figure gives a plan of the apparatus to illustrate its action, when it was worked on the Plenum Principle. In working by exhaustion in the manner already described, all the vitiated air was received at the centre of the fanner, and discharged at the circumference. But in propulsion the fresh external atmosphere was connected with this centre, and the air so received was blown from the circumference into the distribution tubes, and supplied from them to the several compartments of the vessel; and as the medicator (the special arrangement for purifying the air already alluded to,) B was interposed between the windsail which received the external air and the fanner F, it is obvious that any materials placed in B, and capable of influencing the condition of the air, must have been modified in its passage to the decks below. Further, as there was thus induced a plenum within the vessel, the air so introduced escaping by the hatches and by the gunwale-tubes, this discharge, or escape of the air propelled, necessarily tended to prevent the ingress of any air, except what had passed through the medicator in proportion to the amount infused.
But the nature of the poison to be combated was unknown, and therefore it was impossible to predict what the effect of various materials might be. Such materials, therefore, were provided as were known to be most powerful in acting upon those poisonous bodies that have been found in the air, more particularly acids, lime, and chlorine; and to these were added substances capable of influencing the hygrometrical condition of the atmosphere. I do entertain the opinion that had we been fortunate enough to discover the precise nature of the poison, and had it been confined to no very extended district, that by keeping the white men below as much as possible, and steaming rapidly through that situation the medicator might have been brought into much more efficient operation than was possible when, with every attention to experiment that circumstances permitted, no clue as to the constitution of the virus was obtained.
Under the circumstances of the case, however, there was reason to believe that the influence of the poison extended much more widely than had been anticipated, and, as has been already stated, the men were, from unavoidable causes, much exposed on deck; and I must also remark that the emanations from the green wood for the fires were to some constitutions peculiarly offensive.
The medicator consisted essentially of a large iron chest, which could be divided into different compartments by iron shelves or frames of iron wire or other materials, and was capable of acting upon the air supplied to the various sections and cabins of each ship, filtering it from impurities that might be mechanically suspended, and affecting it further by heat, or by the materials with which it was charged. These were placed upon frames or in the cistern below the frames, and the filtering cloths could also be impregnated with various solutions.
Having described briefly the ventilating apparatus, I might now enter into various details connected with its action. But as the manner in which it was worked has occasionally been alluded to elsewhere, it will be sufficient in this place if I now append a copy of the Report presented to Sir William Burnett, the Inspector-general of Naval Hospitals and Fleets, in which I have stated the results to which I was led after a careful consideration of the effects which it produced.
Remarks on the system of ventilation, and on the means adopted to purify the air on board H.M.S. Albert. The power of the fanner in renovating the air, in the compartments below, was abundantly manifest during the passage from England to the coast of Africa. By reducing the diameter of the drum connected with the axis of the blade-wheel within the fanners, 260 revolutions were performed in a minute when the vessel was at full speed, and a proportional number as her progress was slower. Thus a current of fresh atmospherical air was constantly propelled below, capable, by proper adjustment of the valves, of having its force concentrated in one compartment, or even in any one cabin of the ship. When we were at St. Vincent, in the Cape de Verds, the whole of the compartments were cleared and thoroughly cleansed. The process of drying the holds was much accelerated by throwing the whole force of the plenum impulse exclusively upon one division at a time. Under ordinary circumstances, the vacuum impulse or exhaustion from below was sufficient for the purpose of common ventilation.
The medicator or purifying chamber. In reporting upon the use of the medicator I shall confine myself to the results of the experiments made on board of the Albert when in the Niger. These experiments, from circumstances that could not be controlled, were rather limited, but sufficient in my opinion to establish the medicator as a most useful, elegant, and economical medium for subjecting the external atmosphere to the action of chemical and other agents, whether with the view of absorbing carbonic acid and other deleterious matters, as by lime; of chemically decomposing it under certain circumstances of impregnation, as by chlorine; of arresting bodies mechanically suspended in the air; or of altering its hygrometrical condition, by substances capable of removing moisture from, or of imparting humidity to it.
The Albert entered the Nun branch of the Niger on the morning of the 13th of August, 1841, and was anchored for several days just within the bar. From the extreme fineness of the weather, the clear state of the atmosphere, the strong sea breezes, and the height of the river rendering emanations from its banks little likely, it was not considered necessary to open the lime-tanks, or to employ any other substance for the purification of the atmosphere by means of the chamber. Chlorine was, however, diffused over the vessel, from the chloride of lime in plates. When the ship was in the middle stream, the paddles were disconnected from the engines, and the action of the current was sufficient to produce from forty-eight to sixty revolutions of the fanner blades per minute. The valves were adapted to the vacuum impulse until the afternoon of the 19th, when we ascended the river. The arrangements were now as follows. The windsails were hoisted to a height of about fifty feet from the deck, and their lower ends were attached to the inferior lateral openings in the medicator: the upper openings were connected with the deck-tubes by means of air-tight canvass hawses. By these means the air circulated below was obtained from a considerable elevation: it was conducted first into the lower compartment of the chamber, and successively through the others, four in number, filtered through fine bunting, first at the lateral openings, and then through a sheet of the same material stretched across the top tray, next transmitted by the canvass hawses to the deck-tubes, from which it passed into the fanners, whence it was distributed throughout the ship. Within the medicator, chlorine was evolved in the lower compartment, by disengaging it from the chloride of lime, by means of sulphuric acid. On the second tier above there were two hundred weight of fresh lime. The atmosphere between decks was not only impregnated with chlorine, but, as I shall endeavour to show, it was also sensibly drier, and proved to be so by actual hygrometrical observation.
We anchored the first night at the top of Lewis’s creek, which is densely wooded all around. The mangrove abounds, and the distance from the sea is between five and six miles. The sea breeze was still strong.
Aug. 20th. Friday. Plenum impulse all day, chlorine evolved from the lower division of the medicator. The third tier trays were filled with fresh-burnt lime, and in the range above this there were ten pounds of the chloride of calcium. Anchored in the evening near a village: the ship was about 150 yards from the banks on each side, which were thickly wooded.
|Therm.||Dry bulb.||Wet bulb.||Differ.|
|Aug. 20, in mid-stream, 11 p.m.|
|On the upper deck||78.00||77.50||75.00||2.50|
|In the captain’s cabin||83.00||83.00||79.50||3.5|
|In the gun-room||82.00||82.00||78.00||4.00|
|On the lower deck||84.5||84.50||81.00||3.50|
|Aug. 21. 1 a.m. Plenum movement with evolution of chlorine. In the evening anchored (to avoid a swamp) below a village on right bank|
|On the upper deck||77.0||77.00||75.00||2.00|
|In the captain’s cabin||80.5||80.00||76.40||3.60|
|In the gun-room||80.5||80.00||76.40||3.60|
|On the lower deck||84.5||84.50||81.00||3.50|
|Aug. 22. 2 a.m.|
|On the upper deck||78.00||78.00||76.00||2.00|
|In the captain’s cabin||81.50||81.00||77.00||4.00|
|In the gun-room||81.50||81.50||78.00||3.50|
|In the midshipmen’s berth||83.00||83.00||79.50||3.50|
Aug. 23d. Monday. Evolution of chlorine in minute quantity, chloride of calcium, and dry lime on the trays; anchored at 9 p.m. in the middle of the river, about two hundred yards from the banks on each side. Results as before.
Aug. 25th. Chlorine being evolved, dry lime on the third tier of trays. The chloride of calcium being in a state of liquefaction was removed.
|August 25th, 9 a.m.||Therm.||Dry bulb.||Wet bulb.||Differ.|
|On the upper deck||78.5||78.0||76.0||2.0|
|In the captain’s cabin||79.0||79.0||76.0||3.0|
|" lower deck||84.0||84.0||81.0||3.0|
At 12.30 p.m. The filter was removed from the lower lateral openings on each side of the fanner, and found covered with dust, which, examined through a microscope, was found to consist of small vegetable fibres, particles of black matter, fibre from cloth and portions of grass. Three p.m. during a heavy shower of rain when off the village Imbilamma, Mason’s hygrometer indicated as follows. (At the time the experiment was made, the cabin and gun-room were almost wholly supplied with air that had passed through the medicator, the port slides being shut to exclude the rain.)
|Imbilamma, August 25th, 1841.||Therm.||Dry bulb.||Wet bulb.||Differ.|
|On the upper deck||78.0||78.0||76.0||2.0|
|On the upper deck||78.0||78.0||76.0||2.0|
On our arrival at Aboh on the 26th, the same mode was adopted, and the effects were fully as evident as in the former experiments. The fanner was kept going night and day until we reached the town of Egga, where, from the engineers being all sick, there was no one to disconnect the paddles from the engines. On our return down the river, and thence to Fernando Po and Ascension, the exhausting impulse was put on.
As regards the supply of purified air, I would say that, as a general rule, it will be found sufficient in the captain’s cabin and gun-room where there are comparatively few individuals. On the lower deck, however, where there are so many constantly rendering the air unfit for respiration, the quantity of pure air will not be found adequate to the demand. During the medication of the air in the chamber, the closure of the lower-deck hatches could not be tolerated, and the heat was so oppressive at Egga, that we were necessitated to allow the men to sleep on deck.
The air on the lower deck, from the cause mentioned, always contained a proportion of the common atmosphere. How far beneficial were the means adopted for its purification, I do not pretend to determine, but we have every right to presume, from the acknowledged properties of the chemical agents used, that a vitiated atmosphere could not fail to be materially improved by an admixture with air which had been previously subjected to their influence.