Chem'ual Dttonat'wn.'— Tunnel beneath the Tkimes. 473' 



Upon tliefe I prefs the face of an iron hammer, holding the handle with the left hand, and 

 fuddenly Aide the hammer forward fo as to produce a kind of (hock. In this manner the 

 tletonation or noife is iikewife more diflintt, and its force more eafdy determined. Simple 

 comprcffion produces the detonation in many cafes. 



I think it proper to warn thofe who are not familiar with experiments of this kind, 

 that when the operation is performed with more than a grain and a half, or at moft two 

 grains of phofphorus, there will be danger of burning their hands or clothes by the exccfs 

 of this combuftible, which flies off in a burning-ftate. 



I cannot finifh this article without reftoiing to its true proprietor the portion of honour 

 which is due to the difcoverer of the detonating property of the oxygenated muriate by 

 percuffion or flrong friclion, which Citizen Fourcioy has attributed to me in the Me- 

 moir * he has communicated to the National Inftitute, no doubt in confequence of my 

 having mentioned this phenomenon in my edition of the Philofophy of Chemiftry, under 

 the article of Oxygenated Muriates. Profeflbr V/urzer, of Bonn, was the firft who ob- 

 ferved this faft, by triturating with fome force, in a mortar, a mixture, fcarcely weighing 

 a grain and a half, of three parts of the oxygenated muriite of foda and one part of 

 fulphur. He obtained a detonation which rendered him deaf for feveraldays. See Crell'i 

 Chemical Annals for the year 1792, vol. ii. page 402, 



TUNNEL BENEATH THE THAMES. 



Reports, with Plans, Se£lions, &c. of the propofed Dry Tunnel or Paffage from Gravef- 

 end in Kent to Tilbury in JilTex, demonftrating its Practicability, and great Importance 

 to the two Counties and to the Nation at large ; alfo, on a Canal from near Gravefend 

 to Stroud, with fome Mifcellaneous and Praftical Obfervations. By R. Dodd, En- 

 gineer. Quarto. 28 pages, with 3 plates: viz. 1. Plan and Se£lions of the propofed 

 Tunnel. 2. A View of Gravefend and Tilbury, with the Section of the River, (hew- 

 ing the Strata and Depth of Water: and, 3. A Map of the Country within twenty Mile* 

 of Gravefend. London, printed for J. Taylor, 1 798. 



kJOME account of this undertaking was given in this Journal a few months ago. 

 (II. 239.) The prefent Reports will afford fatisfadory information of its detail and 

 progrefs, and the public will hear with pleafure that it is likely to be carried into 

 effeft. 



In the month of May 1798, Mr. DoUd circulated an Introduftory Report or Addrefs 

 to the Nohility, Gentry, &c. of Effex and Kent, in which he ftates that the. extended fcale 

 of commerce on the liver Thames forbids the conftru£tion of a bridge at Gravefend • but 

 that the pradlice of making paffages, tunnels, or drifts under rivers has been adopted to a 

 great extent in various parts of the kingdom ; namely, at the-coal works under the rivers 

 Tyne and Wear, and at Whitehaven under the very ocean ; that a tunnel is adlually in- 

 tended to be made under the mouth of the river Tyne, to anfwer the purpofes of a bridge 

 for carriages and paffengers ; — that the meafure now propofed will favc a circuit of near 



* Pliilofophical Journal, I. 16*, 

 6 fifty 



