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Savery never fitted his boilers with the safety-valve, although it was subsequently used on Savery engines by Desaguliers; and in deep mines he was compelled to make use of higher pressures than his rudely-constructed boilers could safely bear.

The introduction of his machines was, therefore, greatly retarded by the fear, among miners, of the explosion of his boilers; in fact, such explosion did occur on more than one occasion.

20. The Savery engine was improved, about 1716 or 1718, by Dr. Desaguliers, who attached to it Papin's safety-valve, and substituted a jet injection from the stand-pipe into the "forcing-vessels" for the surface condensation of Savery's original arrangement.

21. The Savery engine, however, after all improvement in design and construction, though a working and a useful machine, was still a very wasteful one. The steam from the boiler, passing into the cold, wet water-reservoir or forcing-vessel, was condensed in large quantity, and also to a very serious extent, by coming into actual contact with the water itself.

Papin, who has already been referred to, in 1707 proposed[1] to avoid this loss, to some extent at least, by the use of his piston, which

PSM V12 D038 Papin steam engine 1707.jpg
Fig. 9.—Papin's Steam-Engine, a. d. 1707.

e interposed between the steam and the water, as in Fig. 9, which is copied from a sketch given by Papin himself.

This engine is, in principle, a Marquis of Worcester engine, in which the piston E is introduced to separate the steam from the water which it impels, and thus to reduce the amount of loss by condensation.

This engine was never constructed, except experimentally, however, and is principally of interest in a history of the steam-engine from the fact that it was a useful suggestion to succeeding inventors.

Papin had, as early as 1698, abandoned his earlier but more ad-

  1. "Nouvelle Manière de lever l'Eau par la Force de Feu, mise en Lumière." Par M. D. Papin, Docteur en Médecine, Professeur en Mathematique à Cassel, 1707.