April 28, 1910] 



NATURE 



267 



employed, fern being one of the most common. The ashes 

 of kelp were not only rich in alkali, but contained a large 

 proportion of lime, which was a necessary ingredient. 



The best alkali, known as barilla, soda of Alicante, 

 &c., came from the East, and was produced by burning 

 kali (hence, of course, the name of alkali) plants of the 

 genus Salicornia, or glass wort. This Eastern alkali was 

 certainly used in Venice, Bohemia, and France, and 

 perhaps it may have been imported here also for the better 

 sorts of glass. Saltpetre, either imported or obtained from 

 accumulations of animal and vegetable refuse (nitre-heaps), 

 was also occasionally used. The use of manganese for 

 improving the colour of the glass was well known. 



The most important feature, however, of the English 

 glass manufacture in the middle of the century was 

 certainly the production of what is still known as " flint " 

 glass, and was at the time also commonly called " cristal " 

 or " crystal." This was far whiter and more brilliant 

 than any glass which could then be made by other 

 methods. It was employed chiefly for making drinking- 

 vessels, but also for mirrors. The name " flint " arose 

 from crystal glass having originally been made from 

 crushed flint, which provided a nearly pure form of silica. 

 The so-called " flint " is really a lead glass. The best 

 authorities seem to hold that the use of lead was first 

 proposed in England some time in the seventeenth century, 

 though neither the name of the inventor nor the precise 

 date of the invention is known.* 



Nesbitt thinks the glass-works established by Sir R. 

 Mansell near Newcastle under his patent of 1614 owed their 

 success to the use of lead, and it seems that England had 

 for long a practical monopoly of the manufacture. 

 Hartshorne quotes a French writer as his authority for 

 the statement that in 1760 English flint-glass makers sent 

 four-fifths of their output abroad, the whole of France 

 being supplied with flint glass from England. 



Watch-making. 



During the eighteenth century the art of horology 

 reached a high level in this country. Tompion, " the 

 father of British watch-making," died in 1713, but his 

 friend and successor, Graham, lived until 175 1. Both 

 were buried in Westminster Abbey. Graham invented the 

 mercurial pendulum for compensating variations of 

 temperature, and described it before the Royal Society in 

 1726. The lever compensation pendulum, acting by the 

 different expansions of brass and steel, and commonly 

 called the " gridiron pendulum," was invented by John 

 Ellicott about 1735. In 1728 John Harrison showed his 

 first chronometer to Arnold, who gave him the good advice 

 that he should go back home into the country and perfect 

 it. This he did, and in 1735 he brought it up to London 

 again to enter it in compedtion for the reward offered by 

 an Act of Parliament passed in 1714, which promised 

 lo.oooZ. to the inventor of a chronometer capable of deter- 

 mining, within certain limits of accuracy, the longitude of 

 ships at sea. The following year (1736) the Board of 

 Longitude gave him 500/. after an experimental voyage, 

 and in 1761 the chronometer was more completely tested 

 by a voyage to Jamaica, when the Board awarded Harrison 

 the full prize, though he did not get paid the whole of it 

 until 1769. In 1749 he received the Royal Society's 

 medal. Mudge (1715-94) and Arnold (1734-99) improved 

 Harrison 's chronometers, and practically brought them to 

 their present form.' 



Many of the clocks and watches made by these and other 

 skilled mechanicians of the period are still keeping good 

 time, and the work of these men, though sometimes a 

 little lacking in finish, will bear comparison, not only 

 with that of their contemporaries in other countries, but 

 with that of any who have succeeded them.* 



Salt. 

 In mediaeval England salt was important rather as a 

 food preservative than as a condiment, as it provided the 

 only known means of keeping meat and fish in an edible 



1 Nesbitt, " Glass Vessels in the South Kensington Maseum " (1878) ; 

 Hartshorne, " Old English Glasses " ; " Encyclopjedia Britannjca," &c. 



2 F. J. Britten, " Former Clock and Watch-makers" (1894). 



3 The clock in the meetine room of the Royal Society of Arts was presented 

 to the society in 1760 by Thomas Grignon (1740-84), a clockmaker of con- 

 siderable reputation in his time. It is still an admirable time-keeper, and 

 seems none the worse for its hundred and fifty years' service. 



NO. 2 113, VOL. 83] 



condition. As Thorold Rogers points out,' for five or six 

 months in the year the majority of people lived on salted 

 provisions. They had to eat salted meat or go without 

 meat at all. In Lent everybody had to live on salt fish — 

 an unwholesome diet, which was a fruitful source of 

 disease. The salt, which was always more or less impure, 

 and often dirty, was originally obtained from sea-water 

 all round the coast, evaporated first by solar heat and 

 afterwards by fuel. The manufacture of salt was among 

 the earliest applications of coal. The process was carried 

 out sometimes in pans or ponds with clay bottoms, but 

 in later years in metal evaporating pans heated by coal. 

 Sussex, Devonshire, Shields, Bristol, Southampton, all had 

 large salt works. From the southern coasts salt was ex- 

 ported to France, whence, centuries before, when the 

 manufacture had depended on the heat of the sun, it had 

 been imported. 



The brine springs at Droitwich were certainly utilised 

 before the early part of the eighteenth century. The salt- 

 bearing strata at Northwich are said to have been dis- 

 covered in 1670 in the course of boring for coal. 



It is to be remembered that the idea of making soda 

 from salt, the foundation of all modern chemical industry, 

 had not yet been realised, though it was perhaps in the 

 air. A little later Roebuck, the friend of Black and the 

 associate of Watt, who was the founder of the great 

 Carron works in Scotland and the first maker of sulphuric 

 acid on a commercial scale, ruined himself by various 

 speculations, amongst which was one for making soda 

 from salt." 



Saltpetre. 



Saltpetre or nitre (nitrate of potash) was a very 

 important product, since it was a principal ingredient in 

 the manufacture of gunpowder. It was also used in glass- 

 making and for other purposes. It was first imported 

 from the East, India and Persia. It was made in 

 England and elsewhere in Europe, where it does not occur 

 as a natural product, in " nitre heaps." These nitre heaps 

 were composed of mixtures of animal excrement with wood 

 ashes and lime. The process dates from the time of 

 Elizabeth, when a German named Honrick discovered to 

 the Queen for a sum of 300J. the secret of making " arti- 

 ficial saltpetre." The heap was watered with urine, and 

 after a sufficient time the material was lixiviated, and the 

 salt crystallised out. As time went on, native saltpetre 

 was imported in considerable quantities, and the need for 

 the strenuous search for saltpetre materials passed away, 

 but much was obtained from the nitre heaps at the date 

 with which we are concerned. 



Gunpowder. 



The earliest English gunpowder mills were those estab- 

 lished at Long Ditton, in Surrey, by George Evelyn (John 

 Evelyn's grandfather) about 1590. Another very important 

 powder factory was that at Chilworth, established about 

 1654 ^y the East India Company, or leased by them about 

 that time.* This changed hands several times, was 

 flourishing in the middle of the eighteenth century, and is 

 still at work. There were also mills at Dau-tford and at 

 Battle, in Sussex. Defoe tells us that the best powder in 

 the country was made at Battle. The materials, salt- 

 petre, charcoal, and sulphur, in the same proportions as 

 in modern black powder, were crushed in mills driven by 

 water-power, pestles being used, and later stones. The 

 Waltham Abbey mills, started early in the seventeenth 

 century, were purchased by Government in 1787. The 

 method of manufacture remained unchanged from a very 

 early date until quite recent times, and until the introduc- 

 tion of modern powerful explosives. 



Copperas. 



Copperas (green vitriol, or sulphate of iron) was made 

 at many places in England, and was a product of con- 

 siderable importance. It was used in the manufacture of 

 ink, in dyeing, and as a source of sulphuric acid (oil of 

 vitriol). A certain amount of it was obtained in the 

 manufacture of alum from shale, but the bulk of it was 



1 "Six Centuries of Work and Wages," vol. ii., p. 95. 



2 Smiles, " Lives of Boulton and Watt," p. 152 ; "Industrial Biography 

 p. 13s ; "Diet. Nat. Biog.," Roebuck. 



3 " Victoria County Histories (Surtey)," vol. ii., p. 318. 



