barus.] PREFACE. 21 
time and pains in re-investigating and retesting methods and processes 
which, if more elaborate publications by tbese brilliant experimentalists 
were accessible, would not have been necessary. 
In conclusion I wish to make some reference to the makers from whom 
such special apparatus and supplies as are described in this volume 
were obtained. Mr. William Gruuow, 1 whose accomplishments as a 
mechanician are too well known to need characterizing here, made the 
fine parts of the apparatus for us ; the cathetometer, the manometer 
stand, the micrometer and appurtenances, the revolving muffle, and 
other apparatus being from him. Those parts of the apparatus which 
are of fire-clay — the furnaces, crucibles, tubes, etc.— were obtained from 
Messrs. Hall & Sons. 2 I desire especially to commend the technical 
skill of these gentlemen, as well as the pains and patience which they 
spent in making difficult parts of the work. Capillary tubes of plati- 
num and silver I succeeded in inducing the Malvern Platinum Works 3 
to draw for me. As I do not know whether platinum capillary tubes 
have previously been made, I wish to call attention to the fact that in- 
asmuch as they can be heated to any temperature they are useful for 
many other purposes besides those given in this volume. Apparatus of 
porcelain, viz., air-thermometer bulbs and stems, fire crucibles, tubes, 
etc., were furnished in superior quality from MM. Morlent Freres, 4 an- 
cienne M. Gosse. This firm constructed the standard apparatus for 
Deville and Troost, and their artistic skill is unsurpassed. The porce- 
lain of Bayeux used in their apparatus, besides being of the most re- 
fractory kind, has this additional advantage that its heat-expansion 
constants are known. Bulbs were also successfully made for me by the 
Eoyal Prussian Porcelain Works, 5 at Berlin. .These works are the 
makers of Professor Rieth's and Professor Angler's bulbs. The Saxon 
Porcelain Works, 6 at Meissen, courteously placed duplicates of such 
bulbs as they had already made (Professor Brauu's bulbs) at my dis- 
posal. The glass apparatus, boiling tubes in various open forms, were 
originally made for me by Messrs. Whitall, Tatum & Co., 7 who have 
excellent facilities for annealing glass. Closed forms of boiling tube, as 
well as the reentrant air-thermometer bulb of glass, were constructed 
by Emil Greiner, 8 with his usual accuracy and skill. 
Carl Barus. 
Physical Laboratory, U. S. Geological Survey, 
Washington, January, 1888. 
1 William Grunow, observatory, West Point, N. Y. 
2 Hall & Sons, No. 69 Tonawanda street, Buffalo, N. Y. 
3 Malvern Platinum Works, Jas. Queen & Co., agents, Chestnut street, Philadelphia. 
4 Morlent Freres, No. 8 Rue Martel, Paris, Fiance. 
5 Koniglich Preussische Porzellan Manufactur, Berlin ; M. Andersen, director. 
6 Koniglich Sachsische Porzellan Manufactur, Meissen; F. K. Buttner, director. 
7 Whitall, Tatum & Co., Philadelphia, Pa. 
8 Emil Greiner, No. 63 Maiden Lane, New York. 
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