generally placed with the thicker end slightly raised above the other. Fig. 73 shows clearly how the impregnation is effected. Fig. 73.

The raised end of the log is sawn off with a clean section and covered with the cap (c), which consists of a square board and a ring of tarred rope placed between it and the log. The cap is pressed up against the log by the dog-bolts dd, the free ends of which pass through the batten b and are fitted with screw nuts, An oblique hole (h) is bored, into which is inserted the nozzle of a gutta-percha tube connected with the elevated reservoir of antiseptic liquid. The reservoir is placed about 30 feet above the ground in order to secure the required pressure of one atmosphere. Under this pressure the liquid drives before it the sap in the wood. At first, the pure sap runs out at the other end of the log in a continuous trickling stream. Later on, the sap is mixed with the antiseptic substance, the proportion of which of course increases as the sap remaining in the log diminishes, until no more sap is left. and only water containing the antiseptic substance oozes out. Το ascertain whether the wood is sufficiently impregnated, chips are removed from it from time to time and examined. The impregnation is complete before the liquid that runs out of the log is of the same strength as the solution in the reservoir.

The process is very considerably shortened by impregnating at once logs of double the required length. In this case the log is sawn through the middle for about three-quarters of its thickness. It is then raised in the middle so as to make the cut gape open and a piece of tarred rope is let in along the circumference. On letting go the log, the sides of the cut close tightly upon the rope, and form with it a completely water-tight chamber. A single oblique hole with inserted tube suffices to impregnate both halves of the long log. Fig. 74 renders the preceding explanation clear.

Fig. 74.

Mode of impregnating two lengths of log in a single operation.

To prevent waste of the antiseptic substance, the fluid that runs out from the free ends of the logs falls into gutters g, whence it flows away into the cistern ci at the bottom of the platform. From this, the liquid, after being made up again to full strength and, if necessary, freed from organic matters, is pumped up into the re

servoir above.

The timber-yard is accordingly intersected with a well-devised system of masonry or asphalte gutters.

The substances injected in this manner are principally sulphate of copper and chloride of zinc. The strength of the sulphate solution is 1 of salt to 100 of water.

One important advantage of the hydrostatic method is that it involves only a very small capital outlay and requires no special mechanical skill to work. On the other hand, it has two disadvantages, which are great enough to militate against its general adoption. In the first place, wood in the round has to be used, so that all the portions (at least 30 per cent.), which fall off in conversion, are wasted, and thus a very large proportion of the antiseptic substance is lost. In the second place, as the wood must be green and also have its bark on, no conversion in the forest is possible, and thus cost of carriage is made a very heavy item.

ARTICLE 2. THE PNEUMATIC METHOD.

This method is of English origin. The wood, fully converted, and seasoned or unseasoned (the former the better), is placed in an air-tight chamber. This chamber is completely exhausted with an air-pump, an operation which draws off all the moisture from the wood. This result is aided either by heating the chamber or by filling it, previous to working the air-pump, with steam raised to a temperature of 1121° C. and then condensing the steam to form a vacuum. Into the exhausted chamber the antiseptic solution is allowed to flow in, and, with the aid of a forcing pump, the pressure of the liquid is raised to that of nearly seven atmospheres. At the end of from 45 to 75 minutes the impregnation is complete. The liquid filling the chamber is then drawn off through a pipe at the bottom, and the chamber is opened and the wood taken out. The substances injected in this way are creosote, chloride of zine, sulphate of copper, tar, and ferric tannate. Carbolic acid,

added in small proportions, increases the effectiveness of chloride. of zinc. Creosote is the substance most largely injected by the pneumatic method. In using it the temperature in the chamber is raised to 130° C., and in order that the wood may become perfectly dry, it is kept inside the chamber for about two days before the creosote is let in. The chamber is large enough to hold several tons of wood, and the wood is brought into it on trucks moved on rails.

Another form of the pneumatic method, which is daily gaining on public favour, consists in injecting steam saturated with the

antiseptic substance, instead of using a liquid solution. The wood in the chamber remains exposed to the vapour during 6 to 20 hours.

The pneumatic method possesses advantages which render it the most practical of all those yet invented. There is no waste of wood in it, and the wood may be in any condition of seasoning. On the other hand, it requires very expensive plant, which places its adoption beyond the reach of small capitalists.

ARTICLE 3.-THE IMMERSION METHOD.

This method is the simplest of all. The wood, after it has been thoroughly seasoned, is plunged into a bath containing the antiseptic substance.

The more prolonged the immersion is, the more fully does the wood become impregnated, and hence the more durable does it become; but it has been found that very long immersion has the effect of rendering the wood brittle, and 24 hours are considered sufficient. No portion of the wood should be allowed to remain outside the liquid, so that light wood must be sufficiently weighted to remain below the surface. The higher the temperature of the liquid is, the more rapid and effective is the impregnation. Small pieces of timber may be boiled in the bath.

The substances experimented with in this method are chloride of zinc, sulphate of copper, creosote, sulphate of iron, and tar. The first three, being poisonous, cannot come into general use. The strength of the sulphate of iron solution employed is 15 parts of sulphate to 100 of water. Tar has to be maintained at a temperature of 143° C. during the immersion. Except in the case of thin pieces of timber, or when immersion is prolonged beyond the usual duration, the antiseptic substance seldom penetrates into every portion of the tissues, and at any rate does not penetrate equally everywhere. This is, however, not always a drawback, as impregnation of merely the outside tissues will generally suffice to prevent fungoid growth finding an entrance into the interior.

ARTICLE 4.-PAINTING OVER THE SURFACE OF THE WOOD.

n

Oily and resinous substances i a liquefied condition, if brushed thickly over the surface, enter into and fill up sufficiently the outer tissue to increase very considerably the durability of timber, provided cracks extending beyond the impregnated shell do not form. Timber used under complete exposure to atmospheric influences is tarred with excellent results.

GRAPHIC METHODS OF EXHIBITING THE NATURE OF FOREST SOILS AND CROPS.

In an article which appeared in the Revue des Eaux et Forêts for the 10th June, 1890, Monsieur Marcel Volmerange writes as follows:

"One of the most troublesome portions of a Working-Plan report is the description of the compartments. This requires much minute care on the part of the writer as it does steady attention on the part of the reader, and after all it is extremely difficult from a perusal of it to gather any idea of the forest in its entirety.

"A graphic representation of the elementary composition of the forest would probably give a better general idea of its condition and contents with far less trouble.

"Such a method would consist in showing on a sketch map the principal factors of the crop by conventional signs, different colours being used to show the species of trees, such as the following for example :

Complete crops might be indicated by a continuous line.

"These conventional signs, or such others as might be preferred to them, could be used in various combinations, and would thus enable the composition of the forest in each compartment to be shown with whatever degree of accuracy or detail desirable, and a general idea of the forest as a whole could be gained from a simple inspection of the map.

"In order to complete the description, a few lines would be sufficient to explain the nature of the soil, unless it was thought practicable and not too difficult to show also the quality of soil by a similar method of the conventional signs and colours.

"It would also prove interesting, after the lapse of a certain number of years, to make a new map, using similar signs, which, by comparison with the old map, would at once show the alterations and improvements in the condition of the crops, and would facilitate the determination of the changes required in the treatment.

"In writing these few lines, the writer's idea has been to put forward a plan which, improved and further developed, ought to furnish a simple practical means of showing the composition of forest crops."

It may be interesting to compare the above method with one which has recently been independently worked out in India by the