: I 



CUEMISTIIY. 



VIC. 



ptper ihould be first moistened, so as to facilitate the 

 Erooo.. : and the pnxapiUU will thus be separated fn .111 



which will pass through, and may 



- Ti'. or* >- ' ' "' '"' '' '' 



^^oarSiy 2*S% solvent, so that any 

 Me portion may be removed ; and the washings, as 



they Itemed, are to be added to the liquid already 



not formed, but a coloured liquid 

 >uld be Ukon as to the way in 

 ti the colour U examined. Some liquids afford ft 

 different colour when viewed by transmitted in place of 



rSEoted !> ln uch <**> the bMt pUn v- t * "fT 



Mill portion ,.{ the liquid on to a clean **,* 



or diih when the colour may then readily be noticed. 



Occasionally precipitates will change colour by exposure 



to the air ; at, for instance, the cyanide of iron, the 



of manganase, Ac. Other* will change colour by 



the application of heat e.g., the oxide of zinc all of 



'i, and many other circumstances, must be keenly 



and can-fully noticed. 



CRYSTALLISATION. In many cases in which no pre 

 cipitate is afforded, the process of crystallisation may be 

 employed. By this we are enabled to give the solid 

 body a definite form ; for almost every salt crystallises 

 in some peculiar shape so as to make it recognisable. The 

 followiii" eii'Tiiviug affords an illustration of the fact. 



fit. 71. 



body. A perfect one should bo chosen for this purpose ; 

 and, by such means, enormous crystals of the prussiate 

 and bichromate of potass may be produced. 



DISTILLATION AND SI-III.IMATI-N. These operations 

 differ IM..IV in name than in principle, their object 1- 

 to separate volatile from solid substances. By distilla- 

 tion, water, alcohol, ,t,-., may IKS separated from bodies 

 which may have been dissolved in them. Mercury, in a 

 similar manner, is distilled from its amalgams and ores, 

 and obtained in a pure state. For such purposes, glass 

 retorts are employed when a temperature less than a 

 rod heat is required ; whilst, for other operations, ves- 

 sels of porcelain, iron, or platina must be used, as in 

 the preparation of potassium, sodium, the chloride of 

 aluminium. 



Sublimation can generally be effected by means of 

 flasks or tc^t-tubes. Thus sulphur, arsenic, iodine. 

 may bo volatilised in a manner already mentioned under 

 their separate heads in our previous pages. This opera- 

 tion, however, is by no means common in the course of 

 analysis. 



THE BLOW-PIPE. We have thus given an outline of 

 the leading operations in analysis, and shall now make a 

 few remarks on the blow-pipe, an instrument of great 

 use in experimental chemistry, and by means of which 

 we can get, on the small scale, all the results of the most 

 Em furnace. We can hardly recommend, 



powerfu 



Epwm Salt*. Nitre. 



Now here we observe four different forms of crystals, 

 each of which is readily distinguished from the other. 

 The student may readily produce these crystals by dis- 

 ng each of the salts separately in hot water to 

 . and then placing a drop of each on a piece 

 of window-glax- liquid evaporates, the salt will 



reawume the solid form, and present its characteristic 

 development. 



Tin- process of evaporation is generally carried on in 

 evaporating dishes, heat being applied until a pellicle 

 forms on the surface of the liquid. The vessel is then 

 to be removed to a place where it will not be disturbed, 

 when crystals will gradually be formed. The slower the 

 evaporation is conducted, the more regular will the 

 crystals produced be. By such means, highly soluble 

 and less soluble Raits may be separated. Thus chlorate 

 of potass and chloride of potassium are simultaneously 

 afforded in the production of the chlorate ; but the latter 

 is easily rryitallited away from the former by its greater 

 insolubility. In a similar manner, alum is purified from 

 iron and other substances. The best vessels for crys- 

 tallisation only, are rough glazed earthenware dishes, 

 which, by their uneven surface, assist crystallisation ; 

 whilst for refined experiments, vessels of Berlin porce- 

 lain, silver, or platina, are usually employed. The two 

 last, however, are only needed for special purposes. 

 After a liquid has yielded as many crystals as it can, on 

 fresh evaporation more will be afforded. Occasionally, 

 however, a liquid will actually redissolve crystals which 

 have been formed in it. This arises either from an in- 

 crease of temperature, or from a difference of specific 

 gravity in the upper and lower portions of the fluid. 



Some crystals, when exposed to the air, deliquesce ; that 

 is, they absorb moisture from the atmosphere. This 

 occurs with chloride of calcium, chloride of aluminum. 

 and many other substances. Others lose water, or 

 ifflontef, as in the case of sub-carbonate of soda in 

 crystals (the ordinary "soda" of commerce), which is 

 thereby converted into a powder-like substance. 



Large and perfect crystals may be obtained from a 

 solution by immersing in it a crystal of the crystallising 



Glauber** Salts. 



as the best, 



any form of the instrument ; but, f c >r 

 our own part, always employ either the 

 common tinman's blow-pipe, or that in- 

 d by Dr. Black, which can be ob- 

 tained at any instrument-maker's. 



Much art is required in using the 

 Mow-pipe. The air should be blown 

 from the cheeks only, and not from the 

 chest. By that plan, a person may keep 

 up a continuous stream of air for a long 

 time without fatigue, and the mouth 

 may be replenished with air from the lungs by an 

 operation something like the reverse of swallowing. 

 It is impossible further to describe the method, as 

 practice alone is of use. The object the student 

 should have in view, is that of keeping up the stream 

 of air, free from puffing, and to thereby maintain a 

 steady flame. 



The flame consists of two parts. The inner one ends 

 with a blue colour, at the point of which the most 

 intense heat is produced. The outer flame that is, that 

 farthest removed from the jet affords much less heat, 

 being in direct contact with the external air. The uses of 

 these two flames are accordingly different ; the inner one is 

 employed for reduction, and the outer one for oxidation. 

 A wax or composite candle affords a suitable flame fur 

 the blow-pipe. Small rings of platina wire, uina 



foil, and pieces of charcoal, are needed as supports for 

 the substances to be examined. It must be borne in 

 mind, that the charcoal is employed as a deoxidator 

 that is, for the purposes of reducing oxides to their 

 metallic state ; whilst the ring, or foil of platina, is 

 used to produce beads, A-c If the latin . iyed 



in reduction, the metals would form an alloy in many 

 cases, which would destroy the platina support. The 

 use of the charcoal may easily be seen by placing a little 

 red oxide of lead in a small hole made in the charcoal 

 support by moans of a penknife. If the blue flame be 

 then directed on it, metallic lead will be at once reduced. 

 By means of the blow-pipe, a preliminary examina- 

 tion of many substances may be made, which will save a 

 vast deal of time in MI!^, .jumt processes. This remark 

 especially applies to metallurgical chemistry, and to the ex- 

 aniinatioi ds generally. It should be the ol 



of the young chemist, therefore, tofamtli If, by 



constant | i h t he use of the blow-pipe. He may 



commence by red ne i n charcoal supports, usinj; 



only a minute port ion of ;: . A-e. , for the pin 



The use of the oxidating (lame may similarly be tried on 

 metals. Employing a little borax, cat l>i< 

 he may proceed to produce coloured buttons, by the 

 fusion, at the reducing flame, of those substances, for 



