(b. London. England, 14 June 1877; d. Welwyn Garden City, Hertfordshire, England, 21 January 1958)
Whytlaw-Gray designed and utilized precision techniques for weighing both aerosols and gases, notably radon. The second son of a prosperous Australian businessman, he was educated at Glasgow. From 1896 to 1903 he studied and conducted research under Ramsay and Morris W. Travers at University College, London, beginning a lifelong career in the exact manipulation of gases. In 1903 Gray went to Bonn to continue his redetermination of Stas’s atomic weight of nitrogen; he obtained a value of 14.01 (O = 16), compared with the then current standard of 14.04 and with the more recent standard of 14.008. After obtaining the Ph.D. in 1906, he returned to University college, becoming assistant professor in 1908. In 1911 he incorporated the matronymic Whytlaw to his name, possibly to distinguish himself from a colleague, J. A. Gray.
From 1906 to 1914 Gray measured the physical constants of gases in order to determine their atomic weights. Collaborating with Ramsay in the 1910–1911 classic determinations of the density of niton (now called radon), Gray used a modified Steele-Grant microbalance to weigh the minute quantity available–less than 0.10 cubic mm. The new gravity balance, announced in 1909, was constructed of fused quartz having a counterpoised sealed quartz bulb containing a known quantity of air. Balance was effected by varying the external pressure within the case. Absolute weight as a function of buoyancy could be determined by the original instrument with an accuracy of 10-7 gram, the instrument being about 100 times more sensitive than the Nernst microbalance. In 1910 their experiments yielded an average atomic weight of 220 for radon; they modified this value to 223 on the basis of their 1911 results. By this means they had well estimated the correct order of magnitude.
On the theoretical side, following the then accepted atomic weight for radium of 226.5, Ramsay and Gray in 1910 suggested on genetic considerations the atomic weight of 222.5 for radon. Using the microbalance again the following year, they redetermined the atomic weight of radium to be 226.36, confirming the result of Curie, and derived thereby an independent check on their proposed atomic weight of 222.4 for radon. It was the value they expected (given their value for radium) if radon and helium were the only products of the disintegration of radium. However, after the official adoption in 1916 of 226.0 for radium, based, rather, upon the 1912 results of Hönigschmid, the value 222.0 was eventually assigned to radon.
From 1915 to 1922 Gray was science master at Eton. In 1917 he began a twenty-year series of confidential investigations concerning toxic and other smokes for the War Office. Gray further improved the design of the microbalance and used an ultramicroscope to count the number of smoke particles, determine their sizes, and study their lifetimes. He modified Smoluchowski’s theory concerning the rate of coagulation of homogeneous sols so that it would apply rigorously to gaseous systems. He was also interested in the structure of the coagulating particles and examined the effects of electrification and photophoresis.
In October 1923 Gray succeeded Arthur Smithells at Leeds. While continuing government-sup-ported research on aerosols, he resumed some of his investigations on the compressibilities and densities of simple gases. From 1939 to 1945 Gray led a government inquiry into defense against possible chemical warfare, in addition to serving on the International Committee on Atomic Weights. He retired pro forma in 1942, remaining in office until 1945 and at Leeds until 1950. He continued to improve the microbalance and extended his research to include complex organic gases and vapors. After a brief rest at Coventry, Gray, at seventy-five, resumed his research and consultation at Imperial Chemical Industries in Welwyn Garden City.
I. Original Works. An almost complete list of Gray’s nearly 100 papers and reports is part of the notice by E. G. Cox and J. Hume, in Biographical Memoirs of Fellows of the Royal Society, 4 (1958), 327–339. The best-known papers are the joint communications with Ramsay concerning the dramatic series of density determinations of radon; “La densité de l’émenation du radium,” in Comptes rendus . . .de l’Académie des sciences, 151 (1910), 126–128; and “The Density of Niton (‘Radium Emanation’) and the Disintegration Theory,” in Proceedings of the Royal Society, 84A (1911), 536–550. His work on aerosols is summarized in Smoke: A Study of Aerial Disperse Systems (London, 1932), written with H. S. Patterson.
II. Secondary Literature. F. Challenger, who presented Gray for a degree honoris causa at Leeds in 1950, wrote a note in Nature, 181 (1958), 527; and R. S. Bradley wrote a detailed obituary notice in Proceedings of the Chemical Society (Jan. 1959), 18–20. There is also a brief, unsigned notice in Chemistry and Industry (1958), 134.
The original microbalance is described in B. D. Steele and K. Grant, “Sensitive Micro-Balances and a New Method of Weighing Minute Quantities,” in Proceedings of the Royal Society, 82A (1909), 580–594; and W. A. Tilden and S. Glasstone, Chemical Discovery and Invention (London, 1936), 58–61. The designation “radon” was first suggested by C. Schmidt, in “Perikodisches System und Genesis der Elemente,” in Zeitschrift für anorganische und allgemeine Chemie, 103 (1918), 79–118. The value 235 for the atomic weight of radon was suggested by P. B. Perkins, in “A Determination of the Molecular Weight of Radium Emanation. . .,” in American Journal of Science, 4th ser., 25 (1908), 461–473, on the basis of diffusion evidence.
For a discussion of the nitrogen problem as it appeared at the time, see I. Freund, The Stuck of Chemical Composition (Cambridge, 1904; repr. New York, 1968), 313–316. A contemporary consideration of Gray’s work on radon is in A. T. Cameron, Radiochemistry (London, 1910), passim; and W. Ramsay, The Gases of the Atmosphere, 4th ed. (London, 1915), 283–291. S. C. Lind, in “The Atomic Weight of Radium Emanation (Niton),” Science, 43 (1916), 464–465, argued on genetic considerations that radon should be assigned the atomic weight of 222.0 once 226.0 had been established for radium.
A general treatment of Gray’s early work is included in the account by his brother-in-law M. W. Travers, A Life of Sir William Ramsay, K.C.B., F.R.S. (London, 1956), passim.
Thaddeus J. Trenn