LESSONS IN CHEMI8TEY. 



133 



cnt circular a flat piece of tin or sheet-brans will do as well ; 

 place one hand upon this to prevent it falling off, and with tho 

 other hand lift tho jar and invert it into tho dish. In i 

 it will bo soon that tho jar stands on two pieces of slate, 

 parted with about half an inch between them, thus allowing 

 room for the delivery tube to pass beneath. When a ju: 



of the gas, pass a small plate 

 beneath its month, and lift 

 it out of the water ; it will 

 stand in the plate as long as 

 r* quired, if the hollow of the 

 plate be left' full of water. 

 Another jar should bo stand- 

 ing in the dish ready to bo 

 tilled ; and as with one 

 hand the full one is re- 

 Fig. 17. moved, with tho other tho 

 second one should be placed 

 k> receive the gas. Tho chemical action is expressed and ox- 

 plained in this equation 



KC10,= KC1+0. ; 



that is, potassium chlorate, when heated, becomes potassium 

 chloride and oxygen. 



Do not place the flask on a cold substance while it is hot, but 

 when cold fill it with water ; after a few shakes pour it into a 

 tall jar, and add more water. The potassium chloride is very 

 soluble, and the unaltered MnO, goes to the bottom ; let it 

 stand all night, then pour off the " supernatant liquid ;" fill the 

 jar again with water, and again let the MnO, subside ; pour off 

 the clear water, which contains the last traces of the KC1, and 

 throw the MnO, upon a filter, and afterwards dry it ; it is then 

 fit again for use. This will give the student some practice in 



manipulation, but practi- 

 cally it is not worth the 

 trouble, since the MnO, is 

 so cheap. 



3. Oxygen may be got, 

 when large quantities are 

 required, with more economy 

 from the black oxide of 

 manganese itself; but since 

 great heat is required, an 

 iron bottle must be used, as 

 in Fig. 18. In this bottle 

 the delivery tube is passed 

 through a cork in the end 

 of the pipe. The retort 

 is filled with manganese 

 broken into lumps about tho 

 size of a pea ; then the pipe 

 is screwed in, and, to ensure 



perfect tightness, the screw is luted with white lead. 

 The action is 



3MnO, = Mn,0 4 + O, ; 



that ia, the peroxide has been by tho heat reduced to a lower 

 oxide. 



4. A process which answers well, and which is more economical 

 than that in the second, is the following : Take 3 parts by weight 

 of pulverised potassium bichromate (K,O,2CrO, 1 atom of 

 potash and 2 of chromic acid), and 4 of sulphuric acid (H,S0 4 ); 

 heat it in the Florence flask, and the chromic acid parts with 

 half its oxygen. 



K,O,2CrO, *- 4(H,SO.) = K,,SO 4 + Cr,,3SO 4 + 4H.O + SO. 



The compound under the line is chrome alum. 



Combustion is simply chemical combination, and when this 

 combination is violent, sufficient heat is developed to produce 

 fire. 



The affinities of oxygen are remarkably strong, and it is 

 capable of entering into combination with every body in nature 

 except Fluorine ; therefore fire is generally oxygen entering into 

 combination with tho body burning; though we shall find 

 instances of this phenomenon in which oxygen takes no part. 



In the fires of our houses the oxygen of the air is combining 

 with the coal, which is carbon, to form an invisible gas, car- 

 bonic acid gas (CO,), which passes up tho chimney. Hence we 

 Bay that oxygen is the great supporter of combustion. Of course 

 combustion will be more violent in the pure gas than in the air, 



- 18. 



whore it it dilated with nitrogen. This the following ttuml 

 mcnta will show : 



1. Twist a wire ronnd a piece of charcoal (Fig. 19). Take 

 one of the jar of gw standing on the plate, and replace it 

 in the dish of water ; remove the plate, and in it* place pot the 

 circular piece of 



glass ; lift it 



from the water 



and stand it on 



the table, month 



upwards ; hold 



the charcoal in 



the flame of the 



lamp until some 



parts of it are 



red ; with one 



hand slide the 



glass off the 



mouth of the jar 



sufficiently to 



admit of the en- Fig. 19. 



trance of the 



charcoal, and the charcoal will born brilliantly in forming with 



the oxygen carbonic acid gas (CO,). 



2. Place in the " deflagrating spoon " which in a small metal 

 cup soldered to a piece of wire (Fig. 20) some sulphur ; light it 

 it burns with a pale blue flame ; introduce it into a jar of 

 oxygen it burns brightly into SO, (sulphurous acid), which 

 causes the well-known suffocating smell. 



3. Repeat this experiment with phosphorus. The student is 

 advised to use the red amorphous phosphorus, which is not so 

 inflammable as the stick phosphorus. An intensely brilliant 



light is emitted during the formation of the 

 white fumes, which are phosphoric acid (P,OJ. 

 4. The following experiment is very illustra- 

 tive of the fact that burning U chemical combi- 

 nation. Take a piece of fine iron wire such 

 as that of which " ribbon-wire " is made ; coil 

 it into a spiral, ronnd a pencil ; stick the end 

 of it into as small a piece of cork ae yon can ; 

 dip this into any inflammable liquid, such as 

 naphtha : pass the other end through a hole 

 in a disc of tin ; light the cork, place it in a 

 jar of oxygen, as in Fig. 21, and the wire will 

 burn with beautiful scintillations into Fe,O 4 , 

 which is the same oxide of iron as the lodestone. 

 It is better to fit a piece of cardboard in the bottom of the 

 jar, and leave about an inch of water in it : for the fused oxide 

 is so hot that if it touch the glass the jar will crack. 



From the above modes of preparing oxygen we may take 

 examples of one method of finding what weight of the sob- 

 stance is required to give a certain quantity of another. 

 Take the equation 



KC1O, = KC1 + Oi ; 



the atomic weights of these elements are 



39-1 + 35-5 + 48 = 39-1 + SS'5 + 48 



122-6 = 74-6 + 48. 



That is, from every 122'6 parts by weight of potassium chlorate, 

 48 parts by weight of oxygen come off ; 

 or, from 100, 39*2 come off; that is, 1 

 kilogramme of tho salt gives off '392 of 

 the eras, or nearly | kilogramme. 

 Again 



3MnO, = Mn,O. + O. 



3x55+3x 2x16 = 3x +4xl6+2xl 



261 = 2291-38; 



that is, from 261 parts of manganese 



by weight we get 32 of oxygen, or about -^tj 



J of the weight of the MnO,. Bnt the H 



commercial black oxide of nungsneee 



is seldom very pure, and usually yields Fig. SL 



about half this weight of gas a pound 



giving off about 1,400 cubic inches. The relation bstneea 



volumes and weights will be given in dne time. 



Otone is the allotropio form of oxygen ; that is, it seems to be 

 oxygen in " another form," probably condensed, and therefor* 

 more active. It is produced by the slow oxidation of phosphorus. 

 If a piece of this substance be placed at the bottom of Jar is 



Fig. 20. 



