.90 JUNIOR GRADE SCIENCE 



Odour. A very large number of substances cannot be perceived 

 by the sense of smell and are said to be odourless. Other substances 

 have odours which may be described as : sharp, irritating, pleasant 

 or pungent. A substance like ammonia, which has a well-known 

 odour of its own, is said to have a characteristic odour. 



Form. Certain substances are found in pieces having a regular 

 shape, which is always the same for the same kind of thing ; such pieces 

 are called crystals, and the solids are said to be crystalline. The term 

 crystalline is also applied to all transparent substances like glass. 

 Things which are not crystalline are called amorphous, a word which 

 is made up of two Greek words (a not and morphe form) meaning with- 

 out shape. Mustard, flour, soot, are examples of amorphous things. 



State. Solid, liquid or gas. (See Chapter I.) 



Density. The time available will not permit the pupil to find 

 accurately the density of each substance examined, but he should be 

 able to give an idea of its density from observation. For example, he 

 should have no hesitation in saying that a small piece of lead is very 

 dense and that the density of cork is small. It will be enough in most 

 instances to refer to water as a standard. 



Solubility. If salt or sugar is put in a glass of water and stirred, 

 it will be noticed that the salt or sugar disappears and becomes as far 

 as can be seen a part of the liquid itself. We say that the salt or sugar 

 has dissolved or is soluble, and the liquid is now described as a solution. 

 Substances which will not dissolve in water are said to be insoluble 

 in it. 



As a rule only solubility in water will be tested, but it is well to re- 

 member that many substances which are insoluble in water dissolve 

 in other liquids. Beeswax is insoluble in water, but dissolves in 

 turpentine. 



Hardness. If asked to say in what respects iron differs from soap 

 a pupil would probably mention that it was harder than soap. 



Now consider exactly what is meant by the property of hardness. 

 A stone is hard, so is a piece of iron, and also a piece of wood, but they 

 are not of the same hardness. Some things are harder than others. 



It is often easy to decide which is the harder of two things. For 

 instance, a knife is harder than a piece of wood ; for a thumb- or finger- 

 nail can often be dug into the wood, but a finger-nail cannot be dug 

 into a steel knife. Also, wood can be cut with a knife, but not with a 

 piece of india-rubber, because the india-rubber is softer than the 

 wood. All things which a knife will cut or scratch are softer than 

 the knife, and all things which it will not cut or scratch are harder 

 than it. 



