134 SCIENTIFIC AMUSEMENTS. 



of phosphorus (a very inflammable solid substance, kept under water 

 to prevent its taking fire, which must be handled very carefully 

 with wet fingers) about the size of a large pin's head, and drop it 

 into a small bottle or test-tube, and add a few drops of bisulphide 

 of carbon, an evil-smelling volatile liquid, which has the power of 

 dissolving phosphorus (Expt. 237). Shake up, and when the phos- 

 phorus is dissolved, pour the solution into the bottle containing 

 the chloride of gold ; and then cork the bottle, shake well, and 

 allow the whole to stand some hours. The phosphorus will gradu- 

 ally precipitate the gold, but in finer particles than in the last 

 experiment, in consequence of which the fluid has a blood-red tint 

 when looked through against a bright light. Within certain 

 limits, the weaker the gold solution the better is the result ; a few 

 drops of an ordinary yellow solution of chloride of gold to a pint 

 of water suffices, the best result being obtained when about half a 

 grain of solid chloride of gold is dissolved in a pint of water. 

 Sometimes the colour is more inclined to purple or amethyst than 

 blood-red ; this depends on the size of the particles. When blood- 

 red, they are very fine, and will remain suspended for weeks and 

 months before they subside ; if, however, a little salt be added to 

 the water, its colour changes to purple and the particles subside 

 much more quickly. The possibility of obtaining gold in this 

 form was first discovered by Faraday, whence the term " Faraday's 

 Ruby gold," frequently applied to the blood-red fluid. 



Expt. 137. To precipitate Charcoal from Sugar. In both of 

 the last experiments, the reason why the gold precipitates is that 

 the chemical action taking place between the solution of chloride 

 of gold and the sulphate of iron or phosphorus causes the gold and 

 the chlorine in the chloride of gold to become separated from one 

 another, the gold being set free as a solid powder, and the chlorine 

 converted into other compounds which remain dissolved in the 

 water, just as with the chloride of copper in Expt. 132. In the 

 same sort of way sugar may be regarded as a compound of carbon 

 (charcoal or lampblack) with water, so that by adding to sugar 

 some substance which has a strong tendency to take up water, 

 the sugar becomes "decomposed" or separated into solid black 

 carbon and water. Such a substance is sulphuric acid or oil of 

 vitriol. If this fluid be cautiously poured into its own bulk of 

 strong syrup, much heat is evolved, and steam is thrown off whilst 

 the whole swells up, and becomes black through the separation of 

 impure carbon. 



This experiment should be made in a sink or on the ground 

 outside the house, so that if the vessel containing the syrup breaks 

 with the heat, the corrosive acid will not be spilt where it can 



