282 Dr. R. A. Houstoun on a New 
atomic weight o£ 232, and an approximate specific gravity 
of 7*. 
Assuming this hypothetical member to be radium, the 
combining equivalent of its chloride with silver (CI 35 and 
Ag 108) would be 1*399 in accordance with the determi- 
nations arrived at with the other members of the same series, 
and not 1*371 as determined experimentally for the inter- 
mediate atomic weight 226, recently assigned to radium f. 
XXV. A New Spectrophotometer of the Hiifner Type. By 
Robert A. Houstoun, Ph.D., D.Sc, Assistant to the 
Professor of Natural Philosophy in the University of 
. Glasgow*. 
DURING the past forty years a great number of different 
spectrophotometers have been worked out. This will 
readily be seen by a reference to Kayser's Spectroscopies 
vol. iii. chap. 1, where a complete list is given §. But 
although so much attention has been given to designing and 
testing new instruments, few spectrophotometers have been 
made, and most laboratories are without one. This must in 
part be ascribed to their cost, and also to their construction, 
which usually prevents them from being used for any other 
purpose. The object of the present paper is to describe an 
attachment which may be fitted to any spectrometer or 
spectroscope, converting it into a spectrophotometer, and 
which may be removed at once when the ordinary use of the 
instrument is desired. A method for applying the instru- 
ment to the measurement of absorption in the ultra-violet 
is also described. 
Fig. 1. 
The Hiifner Spectrophotometer j| consists (fig. 1) of a 
-spectroscope, before the slit of which a Grlan-Thompson prism 
* Manchester Memoirs, vol. li. No. 2 (1906). 
t Comptes Bendus, vol. cxlv. p. 422 (1907). 
% Communicated by Professor A. Gray, F.R.S. 
§ This list does not mention the new form of the Konig spectro- 
photometer designed by Dr. Martens (" Ueber eine Neukonstruktion des 
Konigschen Spektralphotoineters," F. F. Martens u. F. Grunbauni, Ann. 
der Phys. xii. p. 984, 1903), and the spectrophotometer of Dr. J. Milne 
(< Nature,' lxxii. p. 391, 1905). 
|| " Ueber ein neues Spectrophotometer " von G. Hiifner, Zs, f. physic, 
Chemie, iii. pp. 562-571 (1889). 
