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; or by holding for an instant near the mouth of a bottle containing Glacial Acetic Acid. In examining a Nitrate Bath for alkalinity by means of the reddened litmus-paper, at least five or ten minutes should be allowed for the action, since the change of colour from red to blue takes place very slowly. REMOVAL OF SILVER STAINS FROM THE HANDS, LINEN, ETC. The black stains upon the hands caused by Nitrate of Silver, may readily be removed by moistening them and rubbing with a lump of Cyanide of Potassium. As this salt however is highly poisonous, many may prefer the following plan:--Wet the spot with a saturated solution of Iodide of Potassium, and afterwards with Nitric Acid (the strong Nitric Acid acts upon the skin and turns it yellow, it must therefore be diluted with two parts of water before use); then wash with solution of Hyposulphite of Soda. Stains upon white linen may be easily removed by brushing them with a solution of Iodine in Iodide of Potassium, and afterwards washing with water and soaking in Hyposulphite of Soda, or Cyanide of Potassium, until the yellow Iodide of Silver is dissolved out; the Bichloride of Mercury (neutral solution) also answers well in many cases, changing the dark spot to white (p. 151). A TABLE SHOWING THE QUANTITY OF ANHYDROUS ACID IN DILUTE SULPHURIC ACID OF DIFFERENT SPECIFIC GRAVITIES. (URE.) +---------+------------++---------+------------++---------+------------+ | |Real Acid || |Real Acid || |Real Acid | |Specific | in 100 ||Specific | in 100 ||Specific | in 100 | |Gravity. |parts of the||Gravity. |parts of the||Gravity. |parts of the| | | Liquid. || | Liquid. || | Liquid. | +---------+------------++---------+------------++---------+------------+ | 1·8485 | 81·54 || 1·8115 | 73·39 || 1·7120 | 65·23 | | 1·8475 | 80·72 || 1·8043 | 72·57 || 1·6993 | 64·42 | | 1·8460 | 79·90 || 1·7962 | 71·75 || 1·6870 | 63·60 | | 1·8439 | 79·09 || 1·7870 | 70·94 || 1·6750 | 62·78 | | 1·8410 | 78·28 || 1·7774 | 70·12 || 1·6630 | 61·97 | | 1·8376 | 77·46 || 1·7673 | 69·31 || 1·6520 | 61·15 | | 1·8336 | 76·65 || 1·7570 | 68·49 || 1·6415 | 60·34 | | 1·8290 | 75·83 || 1·7465 | 67·68 || 1·6321 | 59·52 | | 1·8233 | 75·02 || 1·7360 | 66·86 || 1·6204 | 58·71 | | 1·8179 | 74·20 || 1·7245 | 66·05 || 1·6090 | 57·89 | +---------+------------++---------+------------++---------+------------+ A TABLE SHOWING THE QUANTITY OF ANHYDROUS ACID IN THE LIQUID NITRIC ACID OF DIFFERENT SPECIFIC GRAVITIES. (URE.)