The deleterious effect of copper sulphate on green peas

U 16.801: Sulphate of copper poison SO4 or something in some dried peas he remembered reading of in a cheap eatinghouse somewhere but he couldn’t remember when it was or where.

The use of copper sulphate (CuSO4) in various areas of the food-production industry was a hot topic in the nineteenth and early twentieth century. Traditionally it was sprayed in solution by farmers and cultivators on land to counteract disease such as potato blight and to kill weeds which might otherwise impede the growth of crops. The extent to which it was injurious to plants was a matter of debate. On 16 February 1895 the Freeman’s Journal reported that two years earlier:

The Royal Dublin Society undertook a series of experiments for counteracting disease of the potato crop. It consisted of sulphate of copper and lime mixed with water. This was applied, by means of sprayers, to the under leaf of the plant.

The experiment was deemed a success.

But in 1900 the Weekly Irish Times for 16 June reported some bad news on the use of copper sulphate as a weedkiller:

In all previous spraying the sulphate of copper mixture did the killing off of the weeds in a satisfactory way, and proved to be rather a benefit than an injury to the grain crops... During these experiments trials were instituted on charlock plants growing among such crops as peas, broad beans, carrots, lettuces, mustard, beets, and swedes, and all of these were found to be more or less injured by the application of the solution.

In general the impression was growing that copper sulphate was something of a mixed blessing.

Copper sulphate had another use, too. From at least the mid nineteenth century greengrocers were finding themselves in court throughout Britain and Ireland for selling vegetables, and especially bottled peas, which had been treated with copper sulphate to ensure an attractively vivid green appearance. The London Times and regional papers reported cases throughout the latter part of the century. The Irish papers picked up these reports, such as one published in the Weekly Irish Times on 25 June 1881:

Green peas. – At Liverpool, last week, before Mr Raffles, James Lees was charged on the information of John Baker, with selling green peas which were coloured with sulphate of copper, thus making them injurious to health.

The Food and Drugs legislation did not specifically prohibit this practice, but magistrates used their discretion. A common defence was that the peas had been bottled in France, and bought in good faith; the cases do not seem to be concerned with ‘dried peas’, as Joyce perhaps inaccurately remembers.

It seems that Joyce encountered some reference to the practice, and refers passingly to it in Ulysses. One report appeared in the Weekly Irish Times on 8 April 1905, discussing a case from Londonderry:

Alleged Poisoned Peas. At Londonderry Petty Sessions, on Monday a case was heard in which Messrs. Holmes and Mullin, Ltd., one of the largest wholesale and retail concerns in the north of Ireland, were prosecuted for selling peas to which sulphate of copper had been added.

It was stated that ‘sulphate of copper preserved the appearance of the peas, but it was dangerous to health’. The defendants were fined £3 and costs.

John Simpson

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