A stock solution may be prepared by adding 15 grains of chloride of gold and sodium to 7½ oz. of water. (By a "stock solution" is meant a solution that keeps for a long time, and may therefore be prepared in a large quantity.)
The toning-bath is made by taking 3½ oz. of water and pouring in the gold solution till the mixture will turn blue litmus-paper red. (About half an ounce will be sufficient.) To this mixture add bicarbonate of soda until it turns the red litmus back to blue. This bath should be prepared about half an hour before it is needed for toning. A saturated solution (see first paper on simple chemistry) should be made of bicarbonate of soda, and kept in stock.
Bicarbonate of soda is a fine white powder, soluble in ten parts of water. It is used for neutralizing the excess of acid in gold toning-baths. Natural deposits of bicarbonate of soda are found in Africa, where it is called "trona," and in South America, where it is called "urao." Its chemical formula is HNaCO3.]
Names of chemical elements mentioned and their atomic weight:
| Atomic | ||
| Chemical Element. | Symbol. | Weight. |
| Carbon | C | 12 |
| Chlorine | Cl | 35.5 |
| Gold (Latin name Aurum) | Au | 196 |
| Hydrogen (standard weight) | H | 11 |
| Oxygen | O | 12 |
| Sodium (Latin name Natrium) | Na | 23 |
Hydrogen is the lightest substance known, and an atom of hydrogen is used as the standard weight by which all other atoms of the chemical elements are weighed.
Sir Knight Silas Leon Smith, New Orleans, La., asks for a formula for making paper which can be exposed in the camera like a plate. Calotype-paper is probably the paper which Sir Silas says he has seen described, and which produces a positive picture when exposed in the camera. The process is too long to describe in the space devoted to the "Answers to Querists," but the formula may be found in Wilson's Cyclopedia of Photography, which is in most public libraries. Sir Silas sends a formula for sensitizing paper to produce a red image, for which he will please accept thanks. The formula will soon be published in the Camera Club, and credit given.
Sir Knight Frank Evans, Jun., sends the following formula for developer, which he recommends both for plates and for bromide paper.
EIKONOGEN DEVELOPER.
NO. 1.
Sulphite of Soda (Crystals) 3 oz. Hot Water 45 " Thoroughly dissolve, then add 1 oz. of eikonogen.
No. 2.
Sal Soda 4 oz. Water 15 " To develop, take of No. 1, 3 oz.; No. 2, 1 oz.
This developer can be used over again.
| Sulphite of Soda (Crystals) | 3 | oz. |
| Hot Water | 45 | " |
| Sal Soda | 4 | oz. |
| Water | 15 | " |