Test-papers prepared with porous paper show the red color better than those upon glazed or strongly sized paper. If the quantity of acid present however is small, it is not sufficient in any case simply to dip the paper in the liquid; a small strip should be thrown in, and allowed to remain for ten minutes or a quarter of an hour.
If the paper, on immersion, assumes a wine-red or purple tint, in place of a decided red, it is probably caused by carbonic aid gas: in that case the blue color returns when the paper is washed and held to the fire.
Blue litmus-papers may be changed to the red papers used for alkalies by soaking in water acidified with sulphuric acid, one drop to half a pint.
The Salting and Albumenizing Paper.
SALTING PAPER, ETC.
Take of
| Chloride of ammonium, or pure chloride of sodium | 200 | grains. |
| Water | 10 | fluid oz. |
| Albumen | 10 | fluid oz. |
If distilled water cannot be procured, rain water or even common spring water[L] will answer the purpose. To obtain the albumen, use new-laid eggs, and be careful that in opening the shell the yelk is not broken; each egg will yield about one fluid ounce of albumen.
[L] If the water contained much sulphate of lime, it is likely that the sensitiveness of the paper would be impaired (?).