The art of preserving is a most comprehensive subject, and includes the methods adapted to delay the decomposition, oxidation, or destruction by any other means of all those substances which are useful to man. For facility of reference, as well as systematic treatment, the subject is divided into the following sections:

Charred Paper

Collodion is poured over the charred paper. In a few minutes this dries, and a tough transparent coating is produced, through which the printing, etc, can be seen. Bank-notes and other documents charred by fire have been thus successfully treated. (Scient. Amer.)

Food

The object here will be to avoid such matters as may be found in a handbook of cookery, and to confine attention to the processes which have been devised for wholesale purposes. The subject may be divided into the following heads: -

Beer

(1) Acid sulphite of lime is recommended to be added to beer which has to be kept for a length of time in warm places, or to undergo transmarine exportation; 1 gal. of the aqueous solution (commercial) is added to 1000 gal. beer. (2) Lock wood makes a condensed beer thus: - Beer or stout is taken when fit for drinking, and evaporated in a vacuum pan until much of the water and alcohol is distilled away, and the liquor is reduced to a thick viscous fluid. The alcohol and water pass off in vapour, which is condensed in a receiver attached to the vacuum pan, and the alcohol is obtained by redistilling. This alcohol may be re-mixed with the condensed beer. The beer is reduced to 1/8 or 1/12 of its bulk, according to its strength, and as fermentation is suspended by the heat employed, the condensed mixture keeps good for any length of time in any climate. The process of re-making the beer is also simple, consisting in merely adding the bulk of water originally abstracted, and setting up fermentation by the use of a little yeast.

Within 48 hours the beer may be drawn from the tap for use, or bottled; or may be bottled and charged with carbonic acid gas by an aerating machine.

Marmalade

The manufacture of marmalade is a type of the process carried on in bulk. The peel is removed from the oranges, and their pulp is squeezed, to liberate the juice. The peel is softened by steaming, and is then sliced by revolving knives. The pulp is boiled, and then passed through a "searcher," to remove the tough skin and pips. The juice and sliced peel are then mixed and boiled with lump-sugar in steam-jacketed copper pans. Wherever possible, the appliances used are of oak.

Candied Fruit

The " candied-peel" of citrons, lemons, and oranges is thus prepared: - The fruits are placed in vats, and boiled till soft enough to absorb the sugar. The pulp is then entirely removed and wasted, no attempt having been made to utilize it for the production of essences or vinegar. The peel is put into tubs, and treated with hot syrup of sugar for 10 to 14 days. It is then dried on sieves, in a room heated to 100° F. (38° C). It is finally candied by immersion in a boiling limpid syrup of sugar, left to drain on a sieve over the pan, and again hot-dried and packed. Whole fruits are prepared in a similar manner.

Honey

Honey, according to Vogel, contains on an average 1 per cent, of formic acid. Observing that crude honey keeps better than that which has been clarified, Mylius has tried the addition of formic acid, and found that it prevents fermentation without impairing the flavour of the honey.

Fruit-Juices

Formic acid is said to possess powerful preservative properties, exceeding, when added to acid solutions, even carbolic acid, and to be particularly suitable for adding to fruit juices; about 1/4 to 1/2 per cent, is the quantity requisite to preserve fruit juices, vinegar, glue, ink, etc.

Gum

Hirschberg adds a few drops of sulphuric acid, whereby the lime contained in the gum is precipitated as sulphate; after standing, the mucilage is strained off, and exhibits no tendency to mouldiness even after standing for 18 months. (Les Mondes.)

Urine

In the Lyon Medicate, Weiser recommends the use of nitrite of amy! as a disinfectant and preservative of urine, and states that it is preferable to carbolic acid, as it does not interfere with the tests for albumen.

Vaccine Lymph

Dr.Emil Stern, of Breslau, states in the 'Breslaue artzliche Zeit.," that so far as he has been able to observe, a mixture of 1 per 1000 aqueous solution of thymol preserves vaccine lymph from decomposition, while it does not destroy its specific action, and the mixture is not more irritating than ordinary vaccine matter. It does not appear, however, that thymolized lymph is infallible in its action, it seeming to vary in activity according to its age.