542 



NA TURE 



[April 9 , i! 



preserved for future reference should uncertainty arise re- 

 garding them. There are difficulties in doing this, for it is not 

 easy on a small vessel, when there is any sea on, to keep an 

 ordinary note-book from getting wet. It is most convenient to 

 use cards with memoranda of the observations to be made 

 printed on them, which are kept in a small leather case, and 

 when each card is used, it may be slipped beneath the others, as 

 is done in a date-case. The cards can be conveniently kept in 

 boxes, and may be readily and rapidly referred to at any time. 



2. Determination of the density, — The density of the samples 

 of water collected in the Firth is determined by means of a very 

 delicate hydrometer of the form used on board the Challenger. 

 The hydrometer is made of glass, the tubes for body and stem 

 having been very carefully selected to ensure uniformity of 

 diameter. The instrument has a body of about 5 cm. diameter 

 and 12 cm. long ; the stem is nearly the same length, and has a 

 diameter of 3 mm. The process of making and calibrating the 

 hydrometer has been described in great detail by Mr. Buchanan 

 in his Challenger report on the specific gravity of ocean water 

 (" Challenger Rep. Phys. Chem.," vol. i. pt. ii. pp. 1-4.) 



The hydrometer which has been used at the Marine Station 

 is provided with seven movable weights, which can be attached 

 to the top of the instrument, and so increase the weight of the 

 hydrometer from I50'I478 grms. to I55'8390 grms. through 



thirty-six gradations. The volume of the body and bulb of the 

 instrument is i5o , 207occ. ato° - 3, and its coefficient of expansion 

 is known ; the volume of the 100 mm. into which the stem is 

 divided is CV85 cc, and as it is assumed to be uniform, the 

 volume of each millimetre of the stem is taken as o'ooS5. 



The density of each water-sample was taken twice, by first 

 using a weight that did not immerse more than the lower third 

 of the stem, then adding another to immerse at least two-thirds. 

 A table giving the volume of the hydrometer at every tenth of 

 a degree Centigrade from o' to 25° has been drawn up, and from 

 this table the volume of the body at the observed temperature is 

 taken ; the volume of the stem immersed is got from another 

 table, which gives the value for each half millimetre from o to 

 100. These added together give the total immersed volume, 

 and, the weight being taken from another table and divided by 

 this volume, gives the density at the observed temperature. The 

 mean of the two densities is taken, and reduced from the mean 

 of the two corrected observed temperatures to IS°'56 C. by 

 means of Dittmar's table (" Chall. Rep. Phys. Chem.," vol. i. 

 part I, p. 70). 



Advantage was taken of the double determination of each 

 density and of a number of separate experiments to (i irm an 

 idea of the probable error of an individual determination. The 

 result showed that the probable uncertainty is not more than 



v •: 



^■ : .ns'.ruthep \ 



Stations for water samples:— I. Alloa; 

 (near Inchgarvie) ; VI. Oxcar Be 

 May ; S, Scottish Marine Station 



PART OF THE RlVER AND OF THE FlRTH OF FORTH. (20-fatllOm line : ). 



H. Kincardine; III. Hen and Chickens Buoy (near Grangemouth); IV. Borrowstounnes; ; V. OOF Oueensfer, ' 

 Buoy (near Inchkeith) ; VIII., IX, X., XI. live mile; apart; XII. Isle of 



Inchcolm); VII. Her 



CT00O05, taking pure water as I'ooooo, and that consequently, 

 in considering the relative densities of the water in the Firth, the 

 fourth decimal place is certain. 



The amount of total halogen was determined by Mohr's 

 volumetric method, but, as the probable error was so great as to 

 render the second decimal place in the per milleage uncertain, 

 no teliance can be placed on the results. The largeness of the 

 uncertainty is due, in part at least, to the disadvantageous posi- 

 tion in which the determinations were made — a floating labora- 

 tory where the atmosphere was always more or less laden with 

 saline particles. 



The alkalinity was determined by Tornoe's method with 

 standard solutions of hydrochloric acid and of potash. 



The quantity represented by an alkalinity is very small, 

 although the number used to express it is large. An alkalinity 

 0f50meansth.1t in a litre — say 1026 grammes — there is CV05 

 gramme of carbonic acid as calcium carbonate ; that is, a per- 

 centage of 0'00487, which, from the inaccuracy -of the deter- 

 minations, might vary from crocxiaS to - O0476. 



Notes of Previous Work on Estuaty Water 



In 1816 Dr. Joint Murray read a paper to this Society on the 



composition of sea-water, the samples which he analysed being 



taken from the Firth of Forth near Leith. The paper (Trans. 



R.S.E. for 1816) contains results of great theoretical value, 



which were instrumental in modifying the theory of the exist- 

 ence of salts of different bases and acids in solution, and which 

 altogether changed the mole of analysis of sea and mineral 

 waters. Attention was given more particularly to the solid 

 uents, and no observations seem to have been made by 

 I ir. Murray on the variations in salinity at different parts of the 

 Firth. 



Dr. John Davy published a paper (El. New P. . fount. 

 xxxvi. p. 1) in 1843, on " The Temperature and Specific Gravity 

 of the Water of the Firth of Forth." He examined the tem- 

 perature and density of the water at the end of Leith pier 

 on eight occasions at intervals of about a month. It was 

 Davy's intention to continue the monthly observations for a 

 number of years, but, as he had to leave Edinburgh, they were 

 stopped. Since no particulars as to how the densities wen 

 determined were given, it is impossible to compare them with 

 otheis observed at a later date. 



Dr. Stevenson Macadam investigated the salinity of the Firth 

 of Clyde in 1855 (Brit. Assoc. Reports, 1855, ii. 64). He 

 observed the specific gravity at more than fifty places, and de- 

 termined the total solids and chlorine in each. In subsequent 

 investigations he examined the Firths of Cromarty and Inverness. 

 The results are recorded in the Proceeding': of this Society for 

 1866 (Free. Roy. Soc. Ed., p. 5). 



Prof. Kyle, of Buenos Ayres, made some observations in 



