ON TEACHING CHEMISTRY. 281 
83. How can the composition of water (1) by weight, (2) by volume, be 
determined ? 
4, One of the chief chemical laws states that there is no loss or gain of mass in 
any chemical reaction. Describe two experiments to prove the truth of this law. 
5. Give the preparation and properties of nitric oxide. 
Show how the formula of this gas may be deduced from the following data : 
15°6 ce. of the gas passed over heated Cu gives 7°8 cc. of nitrogen; the weight of 
nitric oxide which fills a certain globe is 3°75 grams, the weight of an equal volume 
of hydrogen being 0:25 gram. 
6. How may the composition of air be determined ? 
Would the composition of air be represented either by the formula N,O or 
N,+0O? Give reasons for your answer. 
7. How is mercury extracted from its ores? Show how (a) the oxides, (4) the 
nitrates may be obtained from the metal. 
8. What is a paraffin? Give the preparation of any paraffin, and state the 
action of reagents upon it. 
PRACTICAL CHEMISTRY. 
[N.B.—Credit will be given for good observations even if the conclusions be 
incorrect, but no credit will be given for experiments not actually made, or for con- 
clusions without the observations on which they are based. | 
1, Find the acid-radicle and the metal in D. 
2. E is a mixture: find its composition. 
3. F is a metallic salt: prepare a few small pieces of the metal (about the size 
of a pin’s head). Find in which of the common acids the metal is soluble, and 
which are its chief insoluble compounds. Enclose one of the pieces of metal you 
obtain in the glass tube, together with a slip of paper with your index number. 
EXAMINATION FOR COMMERCIAL CERTIFICATES. 
InoRGANIC CHEMISTRY. 
Atomic WEIGHTs.—H=1, O=16, N=14, S=32, K=39. 
1. Explain the meaning of the term ‘diffusion,’ and describe some experiments 
by which the phenomena of diffusion in gases can be examined. 
One litre of a certain gas diffuses through an opening in the same time as 
3°74 litres of hydrogen. Calculate the weight of a litre of this gas from the fact 
that a litre of hydrogen weighs ‘0896 gram. 
2. State exactly what you understand by the statements that the equivalent of 
nitrogen is 43 and that of sodium is 28. Describe experiments by which you would 
propose to verify these statements. 
3. A current of electricity is passed for some time through a solution of potas- 
sium sulphate in water, entering and leaving the liquid through platinum plates ; 
the current is then interrupted and the liquid well stirred; describe important 
chemical and physical changes that take place during this experiment. 
4, Describe methods of obtaining hydroxides or oxides of the metals from 
sodium chloride, calcium carbonate, ferrous sulphate respectively. 
5. Express by an equation the reaction that takes place between a basic oxide 
and an acid. 
One litre of ammonia gas measured at 10° C. and 740 mm. is passed into a 
solution of sulphuric acid in water and absorbed by the liquid. Assuming that 
the liquid at the beginning of the experimerit contains4 grams of sulphuric acid, 
calculate the weight of caustic potash needed to exactly neutralise it after the 
absorption of the ammonia. 
_&. Compare and contrast the behaviour of hydrochloric, nitric, and sulphuric 
eae, both concentrated and dilute, as shown in their action on the common 
metals, 
7. What are the reactions which take place when (a) ammonia, (6) ammonium 
