Treatise on general and industrial inorganic chemistry / by Etore Molinari ; third revised and amplified Italian edition translated by Ernest Feilman.
- Ettore Molinari
- Date:
- 1912
Licence: In copyright
Credit: Treatise on general and industrial inorganic chemistry / by Etore Molinari ; third revised and amplified Italian edition translated by Ernest Feilman. Source: Wellcome Collection.
66/734
![We are thiis ablo to deduco tliat in a sulphuric acid factory, if ilicrc is no loss, 100 kilos of sulphuric acid should be obtained per 32-65 kilos of sulphur oinployed, and every manu- facturing procoss will be thè more perfect and regalar thè nearer thè practical yields approximate to those demandod by theory. From thè perceiitage composition of a substance which is deterniined by iiieans of ordinary chemical analysis,^ together with thè determination of its vapour deiisity or of some other method for determining its molecular u eiglit, its formula can be deduced. If, for example, we wish to determine thè formula of water, we commence by making a quantitative analysis (see later, chapter on Water), which allows us to deduce thè percentage composition: H = 11-12 per cent., O = 88-8 per cent. If we now determine the density of water vapour compared with that of air, we find that it is 0-626, and multi- plying this by 28-88, we bave the molecular weight compared with hydrogen, which is 28-88 X 0-626 = 18. In order to now discover in what proportion by weight oxygen and hydrogen enter into 18 parts of water (molecular weight), it will be necessary toestablish some simple proportion, taking into account the percentage composition : 100 : 11-12 (H) = 18 : a; a; = 2 100 : 88-88 (O) == 18 : a;' a;'= 16 The quantities by weight of the individuai elements contained in thè molecule correspond to thè atomic weights of these elements or the multiples of these, in cases where several atoms are present. Thus by dividing these values, x and x', by the atomic weights, we will obtain the number of atoms of these elements contained in a molecule of water. 2 : 1 (atomic weight of H) = 2 = H, 16 : 16 (atomic weight of 0) = 1 = O The Chemical formula of water is, therefore, H-O. The formulse of numerous other inorganic and organic substances are found in the sanie way. This is the simplest method of calculating the formulae' of substances, but it cannot be employed when the molecular weight is not known, and this is then arrived at by indirect methods uhich are often emplo3^ed in organic chemistry, for example, by thè formation of various salts or other deri vati ves. DUALISTIC FORMULA. Lavoisier believed that when a base and an acid combine to forni a salt they retain their primitive constitution in thè new molecule. Freni this idea Lavoisier derived his System of dualistic formulae, which represented molecules of salts. Thus, he wrote the formula of calcinili carbonate as CaO.COa, bccause he supposed the components calcium, CaO (base) and carbon dioxide, CO2 (acid), to exist side by side within the molecule. Sulphuric acid was represented by thè dualistic formula SO3.H2O, bccause it was supposed to contain the separate components SO3 (sulphiu trioxide) and H2O (water). In 1819 Berzelius in his studies on the intimate nature of chemical combinations, bascd 011 the conceptions of Lavoisier and the work of Davy, enunciated an electrolytical theory of dualistic formulai, according to which aU compound substances were composed of two ]iarts with differcnt electric charges, negative and positive, namely, thè acid residue —negative—(oxy-acids were alone well known at that timo, but not the halogen acids) and the basic residue—positive—namely, the metallic oxides, for example : + - + - BaO . SO3 ZnO . CO., &c. Bariuin sulpliatc Zinc carbonate ‘ By analifsis in generai is understood tlio operation of splitting a given substance into any or all of its com- ponentsin order to determine its eoinposit ion ; whilst by syntbesis is understood that Chemical procoss by means of which a complex substance is ol)taincd, starting from other simple substances. Thus analysis is the demo- lition whilst synthesis is thè reconstriiction of onc or more chemical structurcs. Synthesis is often used in order to test thè exactitude of analysis, and vice versa.](https://iiif.wellcomecollection.org/image/b28134187_0068.jp2/full/800%2C/0/default.jpg)
