146 



CHEMISTRY 



liable to sudden and explosive decomposition into 

 chlorine and oxygen. Where the affinity of ele- 

 ments for each other is great, the compounds pro- 

 duced by their union are decomposed with difficulty, 

 and where the affinity is feeble, decomposition is 

 easily effected. See also CHEMISTRY. 



Chemistry. Although chemistry has only 

 taken its place as an exact science based upon 

 accurate experimental investigation within a- com- 

 paratively recent period, yet its origin dates back 

 to the earliest times of philosophical study. It 

 will be convenient to give in the first place a short 

 sketch of the history of chemistry, and then to 

 state some of the principles of the science, illustrat- 

 ing these from the simplest facts. When possible, 

 such illustrations will be chosen as are likely 

 to be not altogether unfamiliar to non-scientific 

 readers. 



Historical Sketch. The word chemistry has 

 come to us from the Greek through the Arabic, 

 as shown in our article ALCHEMY. With regard 

 to the chemistry of the ancients, we know 

 that the ancient Egyptians, Phoenicians, Greeks, 

 and Romans were acquainted with a very con- 

 siderable number of useful substances, and that 

 their processes for preparing some of these did not 

 differ m any essential particular from those now in 

 use. It does not appear, however, that they have 

 left any chemical records behind them, or that they 

 knew anything of the science of chemistry. Several 

 metals were known to, arid employed by, these 

 ancient peoples, who were acquainted with processes 

 for reducing them from their ores. Amongst these 

 metals were gold, silver, mercury, copper, tin, lead, 

 and iron ; whilst they also knew and worked with 

 brass, although they were not aware that it was 

 an alloy of copper and zinc. Various alloys were 

 employed for bronzes for statues, and these usually 

 contained copper, lead, and tin. The processes for 

 manufacturing soap, starch, glass, leather, vari- 

 ous mineral and vegetable pigments, stoneware, 

 and other useful substances, were all known and 

 carried on in very early times; and wine and beer 

 appear likewise to have been prepared and used as 

 beverages long before the process of distillation, 

 which was unknown to the ancients, had been 

 introduced. Vinegar, sulphur, and carbonate of 

 soda were also known. 



We find the application in medicine of many 

 chemical products at a comparatively early period, 

 and the Arabians appear to have been the first 

 who tried to prepare new medicines by chemical 

 methods. Geber, who lived in the 8th century A. D. , 

 is the most noted of the Arabian chemists, and he 

 has left some writings which show us what was the 

 state of chemistry at that early date. Geber knew, 

 for instance, how to make and distil vinegar and 

 nitric acid, and even sulphuric acid was made and 

 used as a solvent by him. He knew, amongst 

 other substances, white arsenic, borax, common 

 salt, alum, sal-ammoniac (ammonium chloride), cop- 

 peras (ferrous sulphate), nitre (potassium nitrate), 

 and corrosive sublimate (mercuric chloride), and 

 was acquainted with a number of their properties. 

 He used almost all the kinds of apparatus that 

 were commonly in use down till the 18th century, 

 and understood the processes of distillation, filtra- 

 tion, sublimation, and crystallisation. In one of 

 his works he describes the construction of furnaces 

 for chemical purposes. 



From the 8th till the 17th century but little 

 real progress was made in chemistry as a science. 

 The new knowledge that was gained during this 

 period was mainly due to the assiduity of the 

 alchemists, who, in their vain search for the philo- 

 sopher's stone, necessarily made useful discoveries 

 from time to time. Many of the alchemists so 

 called were mere tricksters who deceived their 



dupes by more or less clumsy experiments, which, 

 appeared to demonstrate the production of gold 

 from baser metal. Others, however, were really 

 earnest and untiring in their labours, and held the 

 fullest belief in the prospects of the ultimate 

 success of some fortunate worker. The new sub- 

 stances obtained by the alchemists were frequently 

 used in medicine, and it is to these infatuated 

 workers, therefore, that we owe our first knowledge 

 of many potent medicines. The writings of many 

 of the alchemists are preserved, but numbers of 

 them are entirely worthless from a scientific point 

 of view, as the descriptions of processes are mixed 

 up with so much of mystery and extravagance that 

 they present a wholly unintelligible jargon. For 

 more detail, however, regarding this remarkable 

 period in the history of chemistry, see the article 

 ALCHEMY. 



As Geber has been called the patriarch of chem- 

 istry, so Robert Boyle (1627-91) has been called 

 the father of modern chemistry, since it was 

 Boyle who first tried to free chemistry from the 

 trammels of alchemy and to place it upon a true 

 scientific basis. Boyle in his Sceptical Chemist 

 tried to discredit the salt, sulphur, and mercury of 

 the alchemists (as well as the Aristotelian earth, 

 air, fire, and water) as elements or ultimate con- 

 stituents of substances, and he gave a scientific 

 definition of an element. Boyle was an experi- 

 mental investigator of consideVable skill, and to 

 him we owe the introduction of the air-pump and 

 the thermometer into this country. His experi- 

 ments upon the physical properties of gases led to 

 the formulation of the law concerning the relation 

 of the volume of a gas to the pressure, which is 

 commonly known as Boyle's Law. 



Theory in modern chemistry begins with Becher 

 (1635-82) and Stahl (1660-1734). The latter 

 adopted, with some modifications, a theory pro- 

 pounded by the former concerning elements and 

 compounds, and formulated the phlogiston theory 

 of combustion. The views of Becher and Stahl 

 regarding elements were not so enlightened as 

 those of Boyle, and must be considered as retro- 

 grade. Stahl's phlogiston theory ( 1697 ) was at once 

 adopted alniost universally by chemists, and for 

 fifty years it was held to give the full explanation 

 of the phenomena of combustion. According to- 

 this theory phlogiston was a constituent of all com- 

 bustible substances. When a substance burned, 

 the phlogiston made its escape, and the product of 

 combustion was regarded as the other substance 

 with which the phlogiston had been previously 

 united. When a metal such as lead was heated in 

 the air, it lost its phlogiston, and the oxide formed 

 was looked upon as the other constituent of lead 

 besides phlogiston. The process of reduction of 

 lead from its oxide by means of charcoal was the 

 transfer of phlogiston from the charcoal to the lead. 

 It did not present itself to the adherents of the- 

 theory as an absurdity that a metal, in losing its 

 phlogiston on oxidation, gained weight, although 

 some of them at least were aware of trie fact. The 

 idea of gain of matter being a necessary accompani- 

 ment of gain of weight is so familiar to us that we 

 can scarcely realise that it was not always so 

 regarded. To this may fairly be attributed the' 

 persistence with Which the phlogiston theory held 

 its ground for so long a period. 



The Dutch chemist Boerhaave (1668-1738), who' 

 did not accept Stahl's theory, published in 1732 his 

 system of chemistry, which was a compilation of 

 practically all that was known up till that date, 

 collected with great labour from a large variety of 

 alchemical and other writings. 



The interval between the introduction of the- 

 phlogiston theory and its overthrow by Lavoisier in 

 1772-85 was one of great advance in chemical 



