(2) Preservation of Wooden Objects in Liquids.
The expense entailed by this method renders it applicable only to articles of small size.
The preservation of small objects in a flat vessel, the bottom of which is covered with glycerine, has the disadvantage that glycerine extracts organic substances and thus assumes a brown colour. If glycerine is used the object should undergo a thorough preliminary steeping, and the glycerine should be renewed until it remains colourless. Closed cylinders filled with glycerine or a mixture of glycerine and water are not convenient because wood nearly always floats in the liquid. This may be remedied however by the addition of alcohol.
Jenner’s Method[172]. When the objects have been thoroughly cleaned with water, pure alcohol, diluted with water until the specific gravity at 54°F. [12·5°C.] reaches 0·96, is poured over them. After six or eight weeks the alcohol is poured off and replaced by fresh alcohol of the same specific gravity. This alcohol is examined in a year’s time, and should always show a specific gravity of 0·96. The alcohol which has been poured off may be filtered, and if necessary decolourized by animal charcoal; when the specific gravity has been again raised to 0·96, by the addition of fresh alcohol, it may be used again.
The same process is applicable to textile fabrics, yarn, and leather.
Protection against Wood-worms, etc.
All the methods mentioned above will destroy insects and their larvae.
In cases in which it is either impossible or undesirable to use immersion or external application, as for instance in the treatment of objects of dry wood, the larvae may be destroyed by dropping petroleum, an aqueous solution of potassium arsenite, or corrosive sublimate, into the various small openings. This will also help to prevent further attacks.
If solutions are not applied insects may be destroyed by the vapour of carbon bi-sulphide or of crude benzene. These liquids, which are sufficiently volatile at the ordinary temperature, should be placed, together with the objects to be treated, in a closed box.
I have used a similar method for the destruction of wood-worms in Egyptian coffins. The coffin is placed in a large wooden box lined with tin plate. The lid, also lined with tin, is provided with projecting edges, to which strips of felt are glued. The weight of the lid by compressing the felt is sufficient to render the box air-tight. Six or eight glass vessels containing crude benzene are placed at the bottom of the chest and of the coffin itself. It need scarcely be added that the box must not be opened near a fire or light, as the vapour forms an explosive mixture with air; it is in fact advisable to have no light or fire in the room.