[89] I have found that the amount of chlorine is smaller in winter than in summer. In the summer of 1894, 100 c.c. tap-water from the Stralau Waterworks often required 0·8 c.c. silver solution: but at that time stronger disinfectants were used on account of the cholera, and this may have caused the increase of chlorine; for since then, and even at the present time (winter 1898), 100 c.c. tap-water requires 0·5 to 0·6 c.c. silver solution.
[90] It may be here observed that objects of limestone or of earthenware may be numbered or marked at the back in black iron ink, which does not disappear even after prolonged steeping in water.
[91] Lepsius, "Denkmäler aus Aegypten und Aethiopien."
[92] It is scarcely necessary to add that any other form of air-pump may be used.
[93] A powerful pressure of water [in combination with a well-acting pump] may cause the fluid to evaporate with such rapidity as to produce bubbles, but these bubbles are easily distinguished by their size from the minute bubbles of air. To avoid this ebullition, the air should not be pumped out too rapidly.
[95] Flinders Petrie, "Archaeological Journal," Part 45, 1888, p. 88.
[96] Zapon: for further information and references see Appendix.
[97] "Chemische Zeitschrift," ii. 1903, p. 203.
[98] For particulars of the composition and action of Kessler's Fluates (salts of Hydrofluosilicic acid) see H. Hauenstein, "Die kessler'schen Fluate" (2nd ed., Berlin, 1895). The depot is "H. Hauenstein, Berlin N. Reinickendorferstrasse, 2b."
[99] Ger. Patent, No. 31032. The apparatus was one of those used in the moulding room of the Royal Museums for the impregnation of plaster moulds and casts.
[100] In applying the above test it is advisable to add one or two drops of nitric acid before the addition of the barium salt. In this case, too, should any other than distilled water be used for steeping, a preliminary examination should be made to determine the presence or absence of sulphates.
[101] [Pure hydrochloric acid is usually sold in two strengths. Concentrated acid has a strength of about 32%, whilst the "diluted hydrochloric acid" of the Pharmacopoeia is about 10%. The former should therefore be diluted with about 15, the latter with about 4 volumes of water. Transl.]