Sainte Croix, when preparing poison, was accustomed to wear a glass mask; but as this once happened to drop off by accident, he was suffocated, and found dead in his laboratory. Government caused the effects of this man, who had no family, to be examined, and a list of them to be made out. On searching them, there was found a small box, to which Sainte Croix had affixed a written request, that after his death it might be delivered to the Marchioness de Brinvillier, or in case she should not be living, that it might be burnt[126]. Nothing could be a greater inducement to have it opened than this singular petition; and that being done, there was found in it a great abundance of poisons of every kind, with labels on which their effects, proved by experiments made on animals, were marked. When the marchioness heard of the death of her lover and instructor, she was desirous to have the casket, and endeavoured to get possession of it, by bribing the officers of justice; but as she failed in this, she quitted the kingdom. La Chaussée, however, continued at Paris, laid claim to the property of Sainte Croix, was seized and imprisoned, confessed more acts of villany than were suspected, and was in consequence broke alive on the wheel in 1673. A very active officer of justice, named Desgrais, was despatched in search of the Marchioness de Brinvillier, who was found in a convent at Liège, to which she had fled from England. To entice her from this privileged place, which folly had consecrated for the protection of vice, Desgrais assumed the dress of an abbé, found means to get acquainted with her, acted the part of a lover, and, having engaged her to go out on an excursion of pleasure, arrested her. Among her effects at the convent, there was found a confession, written by her own hand, which contained a complete catalogue of her crimes. She there acknowledged that she had set fire to houses, and that she had occasioned the death of more persons than any one ever suspected. She remarked also, that she had continued a virgin only till the seventh year of her age. Notwithstanding all the craft which she employed to escape, she was conveyed to Paris, where she at first denied everything; and, when in prison, she played picquet to pass away the time. She was however convicted, brought to a confession of her enormities, became a convert, as her confessor termed it, and went with much firmness to the place of execution, on the 16th of July, 1676; where, when she beheld the multitude of the spectators, she exclaimed in a contemptuous manner, “You have come to see a fine spectacle!” She was beheaded and afterwards burnt; a punishment too mild for such an offender[127]. As she had been amused with some hopes of a pardon, on account of her relations, when she mounted the scaffold, she cried out, “_C’est donc tout de bon!_[128]”