In 1779, accompanied by his wife, he sailed for Spain, as minister plenipotentiary, in order to secure the concurrence of that kingdom in the treaty with France, recognizing the independence of the United States; and though his diplomatic negotiations were conducted in the most honorable spirit, and with consummate prudence and ability, the object of his mission was finally frustrated by the selfish policy of the Spanish government, in requiring America to surrender the right of navigating on the Mississippi. It was during his residence at the Spanish court, that the desperate financial embarrassments of Congress prompted a measure equally unjust to their representative abroad and hazardous to the national credit. Presuming upon the success of his mission, they had empowered their treasurer to draw on Mr. Jay bills payable at six months, for half a million of dollars. As these bills came in, the minister was placed in a situation of extreme perplexity, but his regard for his country's reputation overcame all private considerations; he adopted the patriotic but desperate expedient of making himself personally responsible for their payment, and his acceptances had exceeded one hundred thousand dollars before any relief came to hand. Mr. Jay's residence in Spain also subjected him to other trials, only less severe than the one just mentioned; the vexatious obstacles placed in way of his negotiations by the Spanish government; the insufficiency of his salary at the most expensive court in Europe; the frequent removal of the court from place to place, at the royal pleasure, involving the absence of his wife, whom, for pecuniary reasons, he was unable to take with him; the death of his young child, and his anxiety for the family whom he had left at home, exposed to the dangers of war, and from whom, for more than a year, not a line had been received, might well have harassed a less sensitive nature than his. The fortitude with which he sustained these annoyances may be seen in a letter written by him about this time to his friend, Egbert Benson, of New-York. It commences thus: "DEAR BENSON: "When shall we again, by a cheerful fire, or under a shady tree, recapitulate our juvenile pursuits or pleasures, or look back on the extensive field of politics we once have trodden? Our plans of life have, within these few years past, been strangely changed. Our country, I hope, will be the better for the alterations. How far we individually may be benefited is more questionable. Personal considerations, however, must give way to public ones, and the consciousness of having done our duty to our country and posterity, must recompense us for all the evils we experience in their cause."