CHEMICAL CHANGES IN THE COMPOSITION OF SEA-WATER. 483 



land are larger and make up a greater part of the deposit. The fine washings noted in 

 the above table usually make up the principal part of the deposit, and consist largely of 

 hydrated silicate of alumina, oxides of iron, and minute particles of quartz, along with 

 highly-altered fragments of felspars and other silicates and rock fragments. The deeper 

 layers of the deposit are very stiff and compact, blue or black in colour owing to' the 

 presence of organic matter and of sulphide of iron, while the immediate surface of the 

 deposit in contact with the superincumbent water is thin, watery, and usually of a light 

 brown or red colour from the higher oxidation of the iron. In the " Challenger " 

 trawlings the bag of the net would frequently be filled with a soft red coloured mud 

 from the surface layers, while the iron frame supporting the beam was covered with 

 patches of a stiff Blue Mud or Clay from the deeper layers. 



In this paper we propose, in the first place, to point out the steps that were taken to 

 obtain samples of the sea-water associated with the Blue Mud at several places on the 

 coast of Scotland, and then to state the results of our investigation into the composition 

 of the sea-salts in these samples, and the changes in composition which take place with 

 varying conditions. 



Methods of procuring Mud- Waters. — In order to procure samples of the water associ- 

 ated with the Blue Mud, we converted a pail into a sort of dredge, and by this means 

 obtained mud from Granton Harbour (in 1 to 2 fathoms), from the Old Quarry connected 

 with the laboratory of the Granton Marine Station (in 3 to 5 fathoms), and from the east 

 side of the Inchgarvie bank below the Forth Bridge (in 16 fathoms). In this way we 

 were able to procure characteristic specimens of the muds at these points. The muds so 

 obtained were all of a deep blue-black colour, which colour they retained so long as 

 protected from oxidation, but on exposure to the air they rapidly took up oxygen, and 

 the colour changed to a rusty brown. 



The mud was at once transferred to a large canvas bag, which was hung up to the 

 rigging of the yacht and allowed to drip. The water thus obtained at definite intervals 

 was collected in stoppered bottles, and subsequently carefully examined in the laboratory. 

 In taking off the filtrates, the 1st portion, consisting of about a litre, was bottled after 

 the bag had dripped nearly an hour ; the 2nd portion was taken about six hours there- 

 after, the quantity being about 1|- litres ; the 3rd, 4th, and 5th portions after 

 intervals of twenty-four hours each, and consisted of about 4 litres, 3 litres, and 1 litre 

 respectively, the quantity decreasing gradually. At each place the total amount of water 

 so obtained was generally about 9 litres from about 100 kilogrammes of mud. As will be 

 presently explained, the 3rd and 4th portions obtained in this manner may be taken 

 as truly representing the water associated with the mud when at the bottom.* 



* During the winter of 1891-92, water was collected in a similar way from the deep basins in the Clyde Sea -Area, 

 The great distance through which the mud had to be hauled to the surface (50 to 70 fathoms) rendered the operation 

 much more difficult than when dealing with harbour mud lying in 1 or 2 fathoms, it being too much washed and mixed 

 with the superincumbent water to give satisfactory results. In order to conduct this work successfully, it would be 

 necessary to construct a special apparatus to bring up the soft mud with the water directly associated with it. The results 

 so far agree with those obtained on the Forth. 



