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nerves to convey pain. It is only when those that convey pleasure are stimulated to excess that we fee a unpleasant sensation. The result of the stimulus of the nerves centres in the hair; now if we can render the brain [?] in proportions as we stimulate the nerves we will certainly not be sensible to pain. By chemisty too we find the proportions in which certain substaners, when mixed from poisons: for instance 1 eq of mercury and 1 eq of chlorine forms coloured but 2eq of chlorine with one of the metal forms corrosive subblement a deadly poison. The word chemistry is of Egytian origin and first used to explain all material phenomena; it was soon however confined to metals, and those who worked in them wre called alcheists. At that time it was supposed that everything was compound of from substances, earth, metals fire and water. It was also thought that gold could be produced from copper as well as it could be obtained from the two black substances oxide of copper and charcoal. Chemistry has a three fold object 1st to ascertain what ingredient a body is composed of. 2nd To [illegible] those ingredients, 3rd To [illegible] what compounds can be formed by these ingredients
Lectured 22nd Cohesion and chem. affinity Cohesion acts among particles of the same kind and producing a substance of the same kind.
Affinity is the force by which particles of different kinds are drawn together and forming a different substance from either of the two.
By this means we analize substances [illegible] a substance for which there is a greater
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attraction by one body than another, As in the case of Lime when combined with Sulphuric acid, the lime unites with the acid, while the Carbonic acid gas escapes.
Of the senses we can apply only two to [illegible] bodies, we can taste them and smell them. Hydrogen gas is combustible but will not support life or combustions , It is lighter than air. Heat is an imponderable agent and gives us the peculiar sensation we feel, when near a fire. The nature of the cause of heat has never been determined. That which best explains the phenomena of heat, is that which supposes a sensible fluid capable of maintaining itself in bodies of the densest nature. He must suppose that the particles of matter are surrounded by an atmosphere of Caloric, between which there is an attraction.
Bodies are of three kinds, solid, liquid, and aeriform. Substances of different kinds at the same temperature, have different quantities of caloric- called thin specific heat thus soapstone has more heat than iron, and those that have more heat, have their [particles?] smaller, Heat increases the bulk of bodies; iron when heated expands and the same takes place with other bodies. The wicks of oil lamps char because oil burns at a high temperature, while the wicks of spirit lamps do not char and require no trimming because the ethereal oil burns at a low temperature.
The reason why dough-nuts are cooked in lard instead of water is that the former may be made hotter than the latter which when the temperature is raised above 212 degrees passes off in steam
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Lectures [?] rd[?] Heat and its properties 'Tis said that there is no heat in fire - The sensation which one feels when he applies his hand to a body warmer than it,
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make it burn, water is therefore better as it not only excludes the air but also conveys away the heat in the form of steam.
We can boil water in a paper vessel as the paper burns about 2,000 degrees, while water boils at 212 degrees, therefore paper cannot get to a higher temperature than the boiling poin t in contact with water
Lecture 24th
Heat and Oxygen Radiant heat is that which is thrown off in [illegible]-lines from a hot body. Rough surfaces will radiate and absorb more heat than a polished surface, because being rough they contain more surface. Smooth surfaces reflect most but radiate and absorb least, hence if we wish to keep anything warm it should be in a bright vessel, but if we wish to heat anything be put in a rough and dark vessel
The quantity of heat peculiar to any body is called specific calorie. Therefore if a pound of mercury and a pound of water at 32° be subjected to the same heat, we will find that the heat required to raise the water one degree will raise the mercury [29ˆ?], this is called the specific calorie of water and it is said to have a greater capacity for heat. Latent heat is that which is employed in changing the form of a body and Free heat is that employed in changing the temperature of anything. If snow and water each at 32ˆ be ehated the water will rise 160ˆ while the temperature of the snow remains unchanged, this heat is employed in keeping the particles apart. The temperature of the celestial regions according to Profs. Henry and Farraday
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is 58ˆ below zero. As we descend in the earth the temperature rises one degree for every forty five feet. Ponderable bodies are such as are capable of being weighed or have appreciable weight. Formerly these were supposed to exist but four elements viz. Earth, Air, Fire, and water. these since have been proved to be compound, and the Chemist can now reduce all bodies to 56 simple substances or elements Oxygen in its simplest state is a gas. It was discovered by Dr. Priestly in 1774 he called it Dephlogisticated air. In 1776, Schul demonstrated [?] Imperial air, Count Dorsy called it vital air, and Lavoisier called it oxygen gas; from two Greek words signifying the former of acids; because it enters largely into the compositions of the acids. It is obtained by heating the peroxides of Lead or Manganese and many other substances as it is the most abundant element in Nature. It is a surporter of combustion if a wire of Iron or steel be heated at one end and placed in a vessel of oxygen it burns with vivid scintillations. Phosphorus where burning in oxygen produces the most brilliant artificial light
Combustion is the union of oxygen which is negative with the particles of a body which is positive but they usually do not unite until heat is applied which increases the intensity the heat is produced by the Chemical Condensation