SUBDIVISION BY SOLUTION. 



If a grain of salt be dissolved in 1000 grains of distilled water, 

 each grain of the water will contain the 1000th part of the grain 

 of salt ; and if a grain of this water be mixed with 1000 grains 

 of distilled water, the 1000th part of a grain of salt which it 

 holds in solution will be uniformly diffused through the latter, so 

 that each grain of the latter solution will contain the 1,000000th 

 part of a grain of salt. The presence of the salt in this second 

 solution can be detected by certain chemical tests. 



It is evident that this process may be continued to a still greater 

 extent. 



24. A grain of sulphate of copper, dissolved in a gallon of 

 water, will impart to the whole mass of the liquid a plainly per- 

 ceptible tinge of blue; and a grain of carmine will give its 

 peculiar red to the same quantity of water. It follows, therefore, 

 that a minute drop of such water will contain such a proportion 

 of either of these substances as the drop bears to the gallon. 



25. The sense of smelling, although it does not inform us of 

 the mechanical qualities of minute masses of matter, determines, 

 nevertheless, their presence : thus, it is known that a grain of 

 musk will impregnate the atmosphere of a room with its odour 

 for a quarter of a century, or more, without suffering any consi- 

 derable loss in its weight. 



Every particle of the atmosphere which produces the sense 

 of the odour must contain a certain quantity of the musk. 



26. The sense of taste, like that of smelling, may determine 

 the presence of matter, without manifesting, by direct evidence, 

 anything concerning its mechanical qualities. 



A portion of strychnine, so minute as to be scarcely perceptible 

 to the sight, dissolved in a pint of water, will render every drop 

 of the water bitter. Now, it is evident that in this case, the 

 strychnine being uniformly diffused through the water, the 

 minute portion of it above mentioned is subdivided into as many 

 parts as there are drops of water in a pint. 



27. In like manner, a single grain of the salt of silver, called 

 ammoniacal hyposulphite, will impart a flavour of sweetness to a 

 gallon of water. Now, a gallon of water will weigh about seventy 

 thousand grains ; and as the flavour of the salt is perceptible in 

 each grain of the water, it follows that one grain of this salt is 

 thus divided into seventy thousand equal parts. 



28. A small lump of sugar, dissolved in a cup of tea measuring 

 half a pint, will sweeten the whole perceptibly. In this half-pint 

 of tea there are thirty-one thousand drops. Each drop, therefore, 

 must contain the thirty-one thousandth part of the sugar dis- 

 solved, and each such drop is perceptibly sweet. But if the point 

 of a needle be inserted in one of these drops, and withdrawn from 



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