These examples, which could be multiplied indefinitely, indicate, in the first place, that every precaution should be taken to store the substances as carefully as possible, and also that, as regards the majority of chemicals which are used, the actual amount of active substance present is very uncertain.
Fortunately, the ordinary photographic pro cesses do not require great precision. A con siderable variation of an active substance in a photographic bath would often pass unnoticed. It i therefore useless to discuss the relative merits of formulae differing from one another in a small degree, since the variations, which occur unknown to the operator, are in many cases much larger.
271. Storage of Chemicals. Many solid sub stances, which are not readily affected, are usually delivered in bags or cardboard boxes, to reduce carriage costs, but there are very few photographic chemicals which, if stored in this manner for any length of time, would not become spoiled to a greater or lesser extent. Moreover, it is not infrequently found that the labels or inscriptions on such parcels are lost or become illegible, or that the bags are split with the consequent risk of annoying losses and mistakes.
Stable substances, such as hvposulphite, alums, and the various natural products, which are occasionally used, gum, starch, etc., should. be stored in wooden boxes, or the bags contain ing them should be placed in labelled metal boxes.
All other substances should be stored in tightly-stoppered glass or earthenware recep tacks. For this purpose, narrow-necked reagent bottles are very much easier to seal hermetically than the ordinary type of wide-mouth bottle. Druggists usually seal off their bottles with flat corks which are cut off level with the neck. This method, although perfect at the outset, does not afford such an airtight joint once the cork has been removed and replaced. It is therefore better to obtain, both for ordinary products and for unstable substances, a series of bottles of required capacity, fitted with good quality cork stoppers of tall conical' shape, which are easily removed by hand, and will last for a considerable time.
It is frequently supposed that ground-glass stoppers are preferable to cork. Although they must of necessity be used with certain liquids, such as nitric and sulphuric acids, which attack both cork and rubber, the fitting so obtained is far from airtight, and there is the additional risk that the stopper will stick tightly unless smeared with paraffin. 2 This type of
stopper should be avoided for alkalis and their solutions, and for very volatile liquids, such as ether.
Many substances which attack cork (solutions of caustic soda and potash, hydrochloric acid, eau de Javelle) can be stored in perfect condition in bottles fitted with rubber stoppers. This method of storage is recommended for all oxidiz able solutions. 3 Beer and preserve bottles can be obtained with mechanical caps, which fit down tightly on to rubber rings. These afford a perfect airtight fit, which is specially useful for oxidizable liquids and solids. It is also possible to procure rubber caps, which may be drawn right over the neck of a bottle fitted with an ordinary cork stopper, in order to render the joint more airtight.
In France, the law demands that in a profes fesional establishment, all poisonous substances (which are always delivered with a red label and a second label marked " Poison ") shall be kept under lock and key in a special cupboard. All other chemicals may be stored on shelves in the room where the baths are prepared. To avoid all chance of dangerous mistakes, no beverages or pharmaceutical products should be kept in this same room.
The amateur must never store photographic chemicals or their solutions near household or pharmaceutical preparations, and it is important that they should be inaccessible to children. Bottles of similar shape to those used for beverages should be avoided, or at least the old labels should be removed and new ones indicat ing the contents made clearly visible. As the common photographic chemicals are not poison ous, their accidental ingestion will have only disagreeable consequences.
272. Labelling of jars and Bottles. The neces sity for labelling very clearly the containers of all substances or their solutions 1 immediately they are bottled cannot be stated too emphatic ally. Neglect of this elementary precaution, especially in a dark-room to which several people have access, leads inevitably to annoying mistakes and to loss of materials which cannot be identified.