428 



• KNOWLEDGE • 



[DEa 1, 1882. 



elements included in older lists were potash, soda, and 

 limr. Sir Humphry Davy, in his electrical experiments, 

 sucx^^li'd in splitting up soda, and obtaining from it tlie 

 mt'tul sodium ; soda was necessarily then relegated from 

 the list of elements to tliat of compounds. Since that 

 time, the attack on the elements luis been sustained with 

 vigour, and during the last year or two the researclies of 

 Mey.r and others have indicated a possibility of decom- 

 posin:: the ih luent chlorine ; should such decomposition be 

 eii.v!. d. chlorine, too, would have to be considered as a com- 

 p<iunii. nithrr than an element At this point an experiment 

 may If sviggested, that, simple though it may seem, will con- 

 sidiT.dily help us in deliuing the further terms. Procure 

 somt- copper in tlie form of very line turnings, or better, as 

 filings mix these with about three times their weight ( £ 

 powd.nd sulphur; notice that, however well mixed, the 

 particles of copper and sulphur are still plainly visible. 

 Put the mixture in the bottom of a Gin. test-tube, which 

 it should till about two inches ; heat it over a Bunsen lamp 

 very carefully : it short!)' commences to glow at the 

 bottom : and then, witliout the assistance of the flame, 

 becomes retl-hot throughout the whole luass. Heat now 

 strongly, and u considerable quantity of sulphur boils oil", 

 and c-ondenses in the upper part of the tube. Allow it <0 

 cool, and a bluish-black substance, very unlike both the 

 sulpliur and the copper, may be taken out This substance 

 reuitiihing is a compound of sulphur and copper. Its 

 api"-;ir.ince and properties are very different from those of 

 the constituent elements, and further, the exact quantity 

 of each present is always definite ; if, as in the experiment 

 tried, an excess of sulphur is used, that excess simply 

 remains unaltered, and is boiled away. This should make 

 clear the essential difference between a «iixture and a com- 

 pound ; the former term is applied to what is simply a 

 mixture, without union, of substances in any proportion ; 

 a ii.inpound is produced by actual condiination of elements 

 in (!• liiiite proportions. The terms, when used in chemical 

 treat i^.-i, have always these meanings attached to them. 



This law of definite proportions is one which, the more 

 chemistrj- is studiwl, is the more seen to underlie all 

 theories of chemistry. On weighing the copper, kc, in 

 the exjHrimcnt mentioned, it will be found that G3 of 

 eopp<r have united with 32 of sulphur to form 95 of 

 sul|>hide of copper. When copper combines with oxygen, 

 it dfN-s so in the proportion of G3 to IC ; and if the whole 

 seri.-s of copper compounds l>e observed, they will be found 

 to contain G3, or a multiple of that weight of copper. For 

 every other element there is also a numlnsr which repre- 

 sents the weight of it entering into a compound. In some 

 cases, however, there are two compounds of the same 

 elements ; thus water consists of 2 by weight of hydrogen, 

 and IG of oxygen, while hydroxyl, or hydrogen peroxide, 

 contains 2 of hydrogen and 32 of o.xygen. Not only, then, 

 dw* chemical combination occur in definite proportions, 

 but whf-n, a.s in this instance, two elements combine in 

 more than one proportion, they do so in multiple propor- 

 tioi, T],. -. and other considerations have led chemists 

 " y to adopt John Dalton's atomic theory. 



' ' matter as consisting of extren)ely small 



" 1 irticles, called atoms, concluded that they 



*• r- t ■• u.Mti Ir-twt^n which chemical action took place. 

 Ao.'.r<l;ng to this theory, when copp-r and sulphur unite, 

 Ih.- ui,ir,n is Wwccn the atoms of each, one to one ; the 

 parti. I. thus pr'Kluced ia termed a molecule; the weights 

 *>■'> and .'12 are also coniiidcred the respective weights of the 

 aU.ms. We have in this theory one which, though not 

 admitting of absolute proof, yet affords a simple explana- 

 tion of all inj,tancc» of chemical combination. There is 

 for »upi>oaing tliat, with the .•lementary IxKliea, 



the atoms unite together, and hence there are elementary 

 as well as compound molecules. 



Anotlier point requires some little explanation, and that 

 is the use of symbols. Chemists usually write the initial 

 letter, or a combination of letters, instead of the full name 

 of the element ; thus, 11 is written for hydi-ogen, for 

 oxygen, ifcc. The letter not merely represents the element, 

 but also exactly one atom of it In writing compounds, 

 the synibols of tlie two or more elements are written side 

 by side ; thus, CuS means a compound of one atom each of 

 copper and sulphur ; ILO a compound of two atoms of 

 hydrogen with one of oxygen. When chemical changes 

 take place, they are generally re])resented by an equation — 

 Cu-f S=;CuS. This means that one atom of copper and 

 one of sulphur produce one molecule of the compound, 

 copper sulphide. 



Readers wishing a fuller explanation of the terms dis- 

 cussed in this paper, will find such given in a text-book 

 on chemistry recently prepared Ijy the writer, and published 

 by Messrs. Longmans >t Co. 



Having now removed some slight ditliculties from our 

 way, we shall be able to proceed in the future with more 

 descriptive papers, taking as our first subject the chemistry 

 of sea-salt 



American Bkass Cleanixi;. — Our American cousins- 

 have marvellous powers of n iin-ention.. An example is 

 given in your Science and Art Gossip of November 3rd, 

 where is repeated the claims made by the United States 

 arsenals to be the possessors [not jiossin.siira,- — usfra only — 

 En.] of the best method in all the world for cleaning 

 brass. It is neither more nor less than the Birminghank 

 process of " pickling," that has been practised beyond tho 

 memory of tin! tildest inhabitant by all the brass-founders 

 antl brass-workers there. The acid is sold retail in all the 

 oil-bhups under tho workshoj) name of " pickleacky " 

 ("acky"is the pet name for aquafortis or nitric acid). 

 Not only is the "ucky" borrowed from Birmingham, but also- 

 the " pail of fresh water and box of sawdust," these being 

 always used. The article, after cleaning as described, is 

 dipped in the " acky " and held there a second or two, then 

 rapidly plunged into the fresh water and dried in sawdust 

 — box-sawdust preferred. I may add that the proportions 

 of nitric and sulphuric acid of tho United States arsenal 

 are not the; best possible. I have had some experience in 

 jjractical pickling, and ha\e found that, except for cheap- 

 ness, a much smaller pro]vortion of sulphuric acid is 

 better. In pickling electro deposits of copper, preliminaiy 

 to bronzing, I prefer unmixed commercial nitric acid, used 

 siitarll)/. This is dearer than the crude impure stuff sold 

 as " pickleacky," and, therefore, not commonly used. — 

 W. Mattieu Wh.liams. 



Western Union Tei.ecmiai-u Company. — Like most 

 other great undertakings, this er)mpany had \n-y small 

 beginnings, but it h.is steadily added line upon line to its 

 network, has brought up comjutitor aft<;r competitor, and 

 has now a lousiness of extraordinary magnitude. In 

 lH71-72the company had 02,033 miles of line, 137,190 

 miles of wire, and .5,237 oflices. The niimlier of messages 

 despatched during the year was 12,111,499, and the 

 receipts were 8, l.'J7,C05 dols., of which 2,790,232 dols. 

 remained in the company's treasury as so much net income. 

 In 1881-82, the company owned 131,060 miles of line, 

 371,308 miles of wire, and 12,008 oflices. The number of 

 t<!legrams despatched was 38,812,347 ; the rough receipts 

 of tlie year were 17,114,10.'} dols., and the net receipts of 

 the twelve months were 7,118,070 dols. The most satis- 

 factory feature in the progress made by the company 

 curing the last ten years is the growth of the net revenue. 



1 



