170 SCIENTIFIC AMUSEMENTS. 



145) be used, or the experiments made in the open air, it is very 

 difficult to avoid inhaling more or less of the gas, and so producing 

 much distressing coughing and irritation; consequently only 

 moderately small quantities of materials should be employed, say 

 1 ounce of manganese dioxide and 4 ounces of hydrochloric acid. 



Although chlorine dissolves somewhat freely in cold water, so 

 that it cannot well be collected at the pneumatic trough in the 

 ordinary way, it is much less soluble in strong brine, especially when 

 warm, so that it may be collected over this fluid without much 

 difficulty. Instead of using hydrochloric acid and manganese 

 dioxide, the following materials may be employed. Mix 4 parts 

 of common salt and 3 of manganese dioxide well together in a 

 mortar ; transfer the mixture to a generating flask, and pour over 

 it a mixture of 8 parts of oil of vitriol and 3 of water, previously 

 mixed together and allowed to cool. Chlorine will be evolved, 

 especially if the materials are slightly warmed from time to time. 



Expt. 181. Another Way of preparing Chlorine. Into a gas 

 generator (fig. 56) put two or three ounces of good bleaching 

 powder (chloride of lime), and then pour diluted hydrochloric acid 

 down the funnel ; chlorine gas will be evolved, as there will not 

 be sufficient water present to keep all the gas generated in solu- 

 tion. For experiments illustrating the chemical properties of 

 chlorine gas and solution thereof in water, vide JS"os. 163, 215, 

 216, 217, 228, &c. (Compare Expt. 162, Caution.) 



Expt. 182. To prepare Cyanogen Gas. Heat in a dry test- 

 tube a few grains of powdered cyanide of mercury ; the substance 

 will behave like oxide of mercury (Expt. 178), i.e., it will split up 

 into two constituents, mercury and cyanogen, the former of which 

 will condense in globules on the sides of the tube in the cooler 

 part, whilst the latter will pass off as a gas of peculiar peach- 

 blossom-like odour and inflammable nature, so that on applying 

 a light to the mouth of the tube the evolved gas will burn with 

 a violet-purple flame. The gas can be collected over water at the 

 pneumatic trough, if the cyanide of mercury be heated in a small 

 test-tube generator like that shown in fig. 73. 



Caution. Cyanogen gas is very poisonous, therefore great care 

 must be taken lest it be inhaled in any quantity. 



Expt. 183. To prepare Nitrogen Gas. Put into a flask 

 about equal weights of salammoniac and sodium nitrite with a 

 little water ; fix in the mouth of the flask a delivery tube, as in 

 Expt. 177 (fig. 69); gently heat the mixture in the flask, and 

 nitrogen gas will be evolved. The action taking place is that the 

 two compounds, ammonium chloride (or salammoniac) and sodium 

 nitrite, react upon one another by double decomposition, forming 



