240 EEPORT— 1889. 



very readily produce effects which are only with difficulty produced by 

 heating — that the chemical agent may produce very powerful effects. 

 The ready expulsion of the carbon oxide of the chalk suggests that other 

 substances not yet studied, such as the metals, when treated with acids 

 may behave in a special manner which will afford information as to their 

 nature. At this point, prior to making the experiments with the acids, 

 an explanation may be given of the names oil of vitriol, spirits of salts and 

 aquafortis ; the processes by which they are made may be described and 

 illustrated, without, however, any attempt being made to explain them 

 from the chemical point of view. The sulphuric acid should be made from 

 green vitriol, and its behaviour on dilution should be demonstrated as 

 well as its use as a drying agent. 



Problem VII. To determine what happens when metals are dissolved in 

 acids. — Iron, zinc, lead, tin, copper and silver may be taken. On pour- 

 ing diluted oil of vitriol on to iron or zinc, the metal dissolves with 

 effervescence ; the gas is collected, and when tested is found to burn. 

 Thus a new gas is discovered, differing from all which have previously 

 been studied, inasmuch as it is combustible ; in order not to interrupt the 

 study of the action of acids on metals, however, its further examination 

 is postponed for a while. Resuming the experiments with metals, lead, 

 tin, copper and silver are found not to be acted upon by diluted oil of 

 vitriol. 



Muriatic acid, in like manner, dissolves iron and zinc and also tin 

 with effervescence, and the gas which is given off in each case exhibits 

 the same behaviour as that obtained from iron or zinc and diluted oil af 

 vitriol. Lead, copper and silver are not appreciably affected. 



Aquafortis is found to dissolve not only iron and zinc but also copper, 

 lead and silver, and to convert tin into a white substance — to attack all 

 the metals in fact, thus justifying its name. The gas which is given off 

 as the metal dissolves is observed to be coloured ; when it is collected 

 over water, however, it is seen to be colourless, and to become coloured 

 on coming into contact with air — oxygen and nitrogen are, therefore, 

 added to portions of the gas over water. In this manner, not only is a 

 new gas discovered, but also a test for oxygen ; and opportunity is afforded 

 of here calling attention to the fact that air behaves exactly as oxygen, 

 that the oxygen in air appears to be unaffected by its association with 

 nitrogen- — that, in fact, it is uncombined. From these experiments it is 

 obvious that metals and acids interact in a variety of ways. Finally, the 

 dissolution of gold and platinum by aqua regia may be demonstrated. 



Problem VIII. To determine what happens when oxides are acted 

 on hy acids. — In the course of the previous experiments a number of 

 oxides have been prepared by burning various metals in air ; these are 

 found to be unchanged by water. The discovery that acids act on metals 

 suggests a trial of the effect which acids will have on their oxides ; so the 

 oxides of zinc, iron, copper and lead are submitted to the action of the 

 three acids previously used. Sulphuric acid is found to dissolve zinc 

 oxide, iron rust and copper oxide, but no gas is evolved ; excess of the 

 oxide may be used, and the filtered liquid concentrated ; the crystals 

 which separate may be examined and compared with those obtained by 

 dissolving the metal in sulphuric acid, &c. Litharge apparently is not 

 changed by sulphuric acid, but red lead is, although not dissolved. 

 Muriatic acid being used, all the oxides are found to dissolve, and in the 

 case of red lead a greenish yellow gas is given off" possessing a most 



