Page:EB1911 - Volume 27.djvu/1036

 Of the evangelical revival, he was well known as the author of The Compkat Duly of Man (London, 1763), a work in which he intended to supplement the teaching embodied in the anonymous Whole Duty of Man. His son, John Venn (1750–1813), was one of the founders of the Church Missionary Society, and his grandson, Henry Venn (1796–1873), was honorary secretary of that society from 1841 to 1873.

VENOSA (anc. , q.v.), a town and bishop’s see of the Basilicata in the province of Potenza, Italy, on the eastern side of Mount Vulture, 52 m. by rail S.S.E. of Foggia, 1345 ft. above sea-level. Pop. (1901) 8503. The castle was built in 1470 by Pirro di Balzo, and contains fouar stables each for fifty horses. Many fragments of Roman workmanship are built into the walls of the cathedral, which is due to him also. The abbey church of SS. Trinità is historically interesting; it was consecrated in 1059 by Pope Nicholas II. and passed into the hands of the Knights of St John in the time of Boniface VIII. (1295–1303). In the central aisle is the tomb of Alberada, the first wife of Robert Guiscard and mother of Bohemund. An inscription on the wall commemorates the great Norman brothers William Iron Arm (d. 1046), Brogo (murdered at Venosa in 1051), Humfrey (d. 1057) and Robert Guiscard (d. at Corfu in 1085). The bones of these brothers rest together in a simple stone sarcophagus opposite the tomb of Alberada. The church also contains some 14th-century frescoes. Behind it is a larger church, which was begun for the Benedictines about 1150, from the designs of a French architect, in imitation of the Cluniac church at Paray-le-Monial, but never carried beyond the spring of the vaulting. The ancient amphitheatre adjacent furnished the materials for its walls.

 VENTILATION (Lat. ventilare, from ventus, wind), the process and practice of keeping an enclosed place supplied with proper air for breathing; and so, by analogy, a term used for exposing any subject to the winds of public criticism. The air which we breathe consists chiefly of two gases, oxygen and nitrogen, with certain small proportions of other gases, such as carbonic acid (carbon dioxide), ozone and argon. Oxygen, which is the active and important constituent, and on which life and combustion depend, forms about one-fifth of the whole, while nitrogen, which is inert and acts as a diluent, forms nearly four-fifths. Of this mixture each adult person breathes some 2600 gallons or 425 cub. ft. in twenty-four hours. In air that has passed through the lungs the proportion of oxygen is reduced and that of carbon dioxide increased. Of the various impurities that are^ found in the air of inhabited rooms, carbonic acid gas forms the best practical index of the efficiency of the ventilation. The open air of London and other large inland towns contains about four parts by volume of the gas in 10,000 of air. In the country, and in towns near the sea, two to three and a half parts in 10,000 is a more usual proportion. Authorities on ventilation usually take four parts in 10,000 as the standard for pure air, and use the excess over that quantity in estimating the adequacy of the air supply. But they differ as to the proportion to which the carbonic acid may be allowed to rise under a good system of ventilation. It is generally admitted that the air in which people dwell and sleep should not under any circumstances be allowed to contain more than ten parts in 10,000. This has been accepted as the permissible proportion by Carnelley, Haldane and Anderson, after an extensive examination of the air of middle and lower class dwellings.

The rate at which an adult expires carbonic acid varies widely with his condition of repose, being least in sleep, greater in waking rest, and very much greater in violent exercise. As a basis on which to calculate the air necessary for proper ventilation we may take the production of carbonic acid by an adult as 0·6 cub. ft. per hour. Hence he will produce per hour, in 6000 cub. ft. of air, a pollution amounting to one part of carbonic acid in 10,000 of air. If the excess of carbonic acid were to be kept down to this figure (1 in 10,000), it would be necessary to supply 6000 cub. ft. of fresh air per hour; if the permissible excess be two parts in 10,000 half this supply of fresh air will suffice; and so on. We therefore have the following relation between (1) the quantity of air supplied per person per hour, (2) the excess of carbonic acid which results, and (3) the total quantity of carbonic acid present, on the assumption that the fresh air that is admitted contains four parts by volume in 10,000:—

Some investigators have maintained that, in addition to an increased proportion of carbonic acid, air which has passed through the lungs contains a special poison. This view, however, is not accepted by others; J. S. Haldane and Lorrain Smith, for instance, conclude “that the immediate dangers from breathing air highly vitiated by respiration arise entirely from the excess of carbonic acid and deficiency of oxygen” (Journ. Path, and Bact. 1892, 1, 175). Carbonic acid, however, is not the only agent that has to be reckoned with in badly ventilated rooms, for the unpleasant effects they produce may also be due, to increase of moisture and temperature and to the odours that arise from lack of cleanliness. Again, though there may be no unduly large proportion of carbonic acid present, the air of an apartment may be exceedingly impure when the criterion is the number of micro-organisms it contains. This also may be greatly reduced by efficient ventilation. Comparisons carried out by Carnelley, Haldane and Anderson (Phil. Trans., 1887, 178 B, 61) between schools known' to be well ventilated (by mechanical means) and schools ventilated at haphazard or not ventilated at all showed that the average number of micro-organisms was 17 per litre in the former, and in the others 152. Results of great interest were obtained by the experiment of stopping the mechanical ventilators for a few hours or days. Tested by the proportion of carbonic acid, the air of course became very bad; tested by the number of micro-organisms, it remained comparatively pure, the number being, in fact, scarcely greater than when ventilation was going on, and far less than the average in “naturally ventilated” schools. This proves in a striking way the advantage of systematic ventilation.

In the ventilation of buildings four main points have to be considered: (1) the area of floor to be provided for each person; (2) the cubic capacity of the room required for each occupant; (3) the allowance to be made for the vitiation of the air by gas or oil burners; and (4) the quantity of fresh air which must be brought

in and of vitiated air that must be extracted for each individual. The first will depend upon the objects to which the room is devoted, whether a ward of a hospital or a school or a place of public assembly. The purity of the air of a room depends to a great extent on the proportion of its cubic capacity to the number of inmates. The influence of capacity is, however, often overrated. Even when the allowance of space is very liberal, if no fresh air be supplied, the atmosphere of a room quickly falls below the standard of purity specified above; on the other hand, the space per inmate may be almost indefinitely reduced if sufficient means are provided for systematic ventilation. Large rooms are good, chiefly because of their action as reservoirs of air in those cases (too common in practice) where no sufficient provision is made for continuous ventilation, and where the air is changed mainly by intermittent ventilation, such as occurs when doors or windows are opened. With regard to the third point, in buildings lighted by gas or oil the calculations for the supply of fresh and the extraction of foul air must include an allowance for the vitiation of air by the products of combustion. The rate at which this takes place may be roughly estimated in the case of gas by treating each cubic foot of gas burnt per hour as equal