John McCrae, a chemist by profession, studied at the Royal Technical College in Glasgow, was Priestly Scholar at the University of Birmingham, also studied at the University of Cincinnati in the United States, and obtained the degree Doctor of Philosophy (PhD) at the University of Heidelberg, Germany. He was a Fellow of the Institute of Chemistry and of the Chemical Society, and lectured on chemistry in the United Kingdom from 1895 to 1903. Early in his career he published some chemical papers in German journals and translated two German textbooks into English, namely Outline of physical chemistry (1899, by S.A. Arrhenius) and Text-book of electrochemistry (1902, by A. Reychler).
In November 1903 McCrae came to the Transvaal Colony to take up an appointment as assistant chemist in the Division of Chemistry of the Department of Agriculture, Pretoria, under H. Ingle*. In 1905 he was transferred to the Government Public Health Laboratory at Johannesburg to succeed Dr W.C.C. Pakes* as government analyst for the Transvaal Colony, though initially in an acting capacity. Around that time he published some short articles in the Transvaal Agricultural Journal on eucalyptus oil (1905, 1906), ethereal oils (1906), the liming of soils (1906) and tobacco by-products (1906).
By 1906 McCrae was a member of the South African Association for the Advancement of Science, serving on its council from 1907 for several years, and as general treasurer for 1907/8. A paper by him on "The tracing of underground waters" was published in the association's Report for 1907 (pp. 47-53). Later he was the scientific editor of South Africa and Science (Johannesburg, 1929), a book published by the association in preparation for the meeting of the British Association in South Africa in 1929.
After the formation of the Union of South Africa in 1910 McCray became assistant chief of the Division of Chemistry of the Union Department of Agriculture, a post he held until his retirement in 1929, and was stationed in the Government Laboratory in Johannesburg. For some time he was associated also with the South African Institute for Medical Research and was the author of its Publication No. 3 (1913) on The ash of silicotic lungs. In this paper he described a method for extracting dust from the lung tissue of deceased mine workers, and the nature of the dust so extracted. It proved to consist mainly of silica particles, most of which were smaller than one micrometer.
McCrae was a foundation member of the South African Association of Analytical Chemists in 1912 and was elected as its first president. He served as president again for 1919/20, a year before the association changed its name to The South African Chemical Institute. Alltogether he was a member of council of the association and the institute from 1912 to 1931, serving as treasurer for several years and as vice-president for 1916/7. He was still a member of the institute by 1958. Some of the papers he published in its Journal dealt with Acokanthere venenata (Bushman's poison bush; 1918), chemical nomenclature (1919), manganese in hair (1923), and chemical specification tolerances (1925).
In 1927 McCrae was president of the Associated Scientific and Technical Societies of South Africa. He was also an active member of the Chemical, Metallurgical and Mining Society of South Africa and the South African Association of Assayers. In 1917 he was a member of the original Commission of Examiners for the Government Certificate of Competency in Assaying. After his retirement he became chemist to the Rand Water Board until his final retirement in 1947, at the age of 72. During this period he published a paper on "Suspended solids in the water of the upper Vaal River" (Civil Engineering, 1945). He was survived by his wife Mary Walbrand McCrae, a son and a daughter.