In the directions for preparing printing-paper for violet prints the directions for the coloring-bath read as follows:
SEL D'OR (DOUBLE SALTS OF GOLD).
| Sel d'or | 7½ | grs. |
| Distilled water | 15 | oz. |
| Hydrochloric acid | 1 | drachm. |
A member of the Camera Club, wishing to try the formula, wrote to the editor that he went to a druggist for the "sel d'or," but was unable to obtain it, nor could the druggist tell him what it was. An explanation was sent by mail, but we repeat it for the benefit of the club. "Sel d'or" is a double salt of hyposulphite of soda and gold chloride. It is formed by adding chloride of gold to a hyposulphite solution, and mixing with alcohol. Take three parts of concentrated solution of chloride of gold and one part of concentrated solution of hyposulphite of soda. Mix thoroughly, and add alcohol till it is well covered. Shake well, and then set it aside. The alcohol will cause the chloride of gold and sodium sulphite to be precipitated in the form of delicate needlelike crystals, almost transparent, and readily dissolved in water.
If one cannot, obtain "sel d'or" ready prepared, it is not much work to prepare it. This double salts of gold is the form in which gold was used for toning daguerreotypes in the early days of photography. The silvered plate on which was the picture was coated with a solution of "sel d'or," and then heated. The gold was melted or decomposed by the heat and deposited on the picture, giving it not only a beautiful tone, but also preserving it. That this preparation made the picture durable is shown from the fine daguerreotypes which, though taken so many years ago, still retain almost their first freshness.
Sir Knight W. Baker asks if there is any difference between a sulphite and bisulphite. A sulphite is a salt formed by the union of sulphurous acid with a base. For instance, sulphite of soda is a salt formed by the union of sulphurous acid and sodium, the sodium being the base. A bisulphite is a sulphite in which the metal has replaced but half the hydrogen in the acid. "Bi," used chemically, means that the compound contains two equivalents of the substance named.
Sir Knight Lester R. Moss asks which camera to buy—a "B." daylight or a Kodak, both same price. Would advise a Kodak with glass plates for a beginner. A camera in which films are used is not so satisfactory as one for glass plates, and one can learn how to manage a camera much better if plates are used. Sir Knight Lester asks how he may become a member of the Round Table. Your name has been placed on the membership list. To become a member all that is required is that one should send name and address, and state that he wishes to become a member.
Sir Knight F. G. Clapp sends grateful acknowledgment for query answered in the Round Table for March 31.
Will Max Miner be kind enough to write to the editor and give the name of the camera which he used in making the picture, reproduced in the Round Table, called "Sweeping a Sliding-Place"? A member of the Camera Club is anxious to know. Will Sir Max also add the name of lens and plate used?
[THE PUDDING STICK.]
This Department is conducted in the interest of Girls and Young Women, and the Editor will be pleased to answer any question on the subject so far as possible. Correspondents should address Editor.